Editing Module:Multilingual

local Multilingual = { suite   = "Multilingual",
                       serial  = "2020-12-10",
                       item    = 47541920,
                       globals = { ISO15924 = 71584769,
                                   WLink    = 19363224 }
                     }
--[=[
Utilities for multilingual texts and ISO 639 (BCP47) issues etc.
* fair()
* fallback()
* findCode()
* fix()
* format()
* getBase()
* getLang()
* getName()
* i18n()
* int()
* isLang()
* isLangWiki()
* isMinusculable()
* isRTL()
* message()
* sitelink()
* tabData()
* userLang()
* userLangCode()
* wikibase()
* failsafe()
loadData: Multilingual/config Multilingual/names
]=]
local Failsafe   = Multilingual
local GlobalMod  = Multilingual
local GlobalData = Multilingual
local User       = { sniffer = "showpreview" }
Multilingual.globals.Multilingual = Multilingual.item



Multilingual.exotic = { simple = true,
                        no     = true }
Multilingual.prefer = { cs = true,
                        de = true,
                        en = true,
                        es = true,
                        fr = true,
                        it = true,
                        nl = true,
                        pt = true,
                        ru = true,
                        sv = true }



local foreignModule = function ( access, advanced, append, alt, alert )
    -- Fetch global module
    -- Precondition:
    --     access    -- string, with name of base module
    --     advanced  -- true, for require(); else mw.loadData()
    --     append    -- string, with subpage part, if any; or false
    --     alt       -- number, of wikidata item of root; or false
    --     alert     -- true, for throwing error on data problem
    -- Postcondition:
    --     Returns whatever, probably table
    -- 2020-01-01
    local storage = access
    local finer = function ()
                      if append then
                          storage = string.format( "%s/%s",
                                                   storage,
                                                   append )
                      end
                  end
    local fun, lucky, r, suited
    if advanced then
        fun = require
    else
        fun = mw.loadData
    end
    GlobalMod.globalModules = GlobalMod.globalModules or { }
    suited = GlobalMod.globalModules[ access ]
    if not suited then
        finer()
        lucky, r = pcall( fun,  "Module:" .. storage )
    end
    if not lucky then
        if not suited  and
           type( alt ) == "number"  and
           alt > 0 then
            suited = string.format( "Q%d", alt )
            suited = mw.wikibase.getSitelink( suited )
            GlobalMod.globalModules[ access ] = suited or true
        end
        if type( suited ) == "string" then
            storage = suited
            finer()
            lucky, r = pcall( fun, storage )
        end
        if not lucky and alert then
            error( "Missing or invalid page: " .. storage )
        end
    end
    return r
end -- foreignModule()



local fetchData = function ( access )
    -- Retrieve translated keyword from commons:Data:****.tab
    -- Precondition:
    --     access  -- string, with page identification on Commons
    --     Returns table, with data, or string, with error message
    -- 2019-12-05
    local storage = access
    local r
    if type( storage ) == "string" then
        local s
        storage = mw.text.trim( storage )
        s = storage:lower()
        if s:sub( 1, 2 ) == "c:" then
            storage = mw.text.trim( storage:sub( 3 ) )
            s       = storage:lower()
        elseif s:sub( 1, 8 ) == "commons:" then
            storage = mw.text.trim( storage:sub( 9 ) )
            s       = storage:lower()
        end
        if s:sub( 1, 5 ) == "data:" then
            storage = mw.text.trim( storage:sub( 6 ) )
            s       = storage:lower()
        end
        if s == ""  or  s == ".tab" then
            storage = false
        elseif s:sub( -4 ) == ".tab" then
            storage = storage:sub( 1, -5 ) .. ".tab"
        else
            storage = storage .. ".tab"
        end
    end
    if type( storage ) == "string" then
        local data
        if type( GlobalData.TabDATA ) ~= "table" then
            GlobalData.TabDATA = { }
        end
        data = GlobalData.TabDATA[ storage ]
        if data then
            r = data
        else
            local lucky
            lucky, data = pcall( mw.ext.data.get, storage, "_" )
            if type( data ) == "table" then
                data = data.data
                if type( data ) == "table" then
                    GlobalData.TabDATA[ storage ] = data
                else
                    r = string.format( "%s [[%s%s]]",
                                       "INVALID Data:*.tab",
                                       "commons:Data:",
                                       storage )
                end
            else
                r = "BAD PAGE Data:*.tab &#8211; commons:" .. storage
            end
            if r then
                GlobalData.TabDATA[ storage ] = r
                data = false
            else
                r = data
            end
        end
    else
        r = "BAD PAGE commons:Data:*.tab"
    end
    return r
end -- fetchData()



local favorites = function ()
    -- Provide fallback codes
    -- Postcondition:
    --     Returns table with sequence of preferred languages
    --     * ahead elements
    --     * user (not yet accessible)
    --     * page content language (not yet accessible)
    --     * page name subpage
    --     * project
    --     * en
    local r = Multilingual.polyglott
    if not r then
        local self = mw.language.getContentLanguage():getCode():lower()
        local sub  = mw.title.getCurrentTitle().subpageText
        local f    = function ( add )
                         local s = add
                         for i = 1, #r do
                             if r[ i ] == s then
                                 s = false
                                 break -- for i
                             end
                         end -- for i
                         if s then
                             table.insert( r, s )
                         end
                     end
        r = { }
        if sub:find( "/", 2, true ) then
            sub = sub:match( "/(%l%l%l?)$" )
            if sub then
                table.insert( r, sub )
            end
        elseif sub:find( "^%l%l%l?%-?%a?%a?%a?%a?$" )  and
               mw.language.isSupportedLanguage( sub ) then
            table.insert( r, sub )
        end
        f( self )
        f( "en" )
        Multilingual.polyglott = r
    end
    return r
end -- favorites()



local feasible = function ( ask, accept )
    -- Is ask to be supported by application?
    -- Precondition:
    --     ask     -- lowercase code
    --     accept  -- sequence table, with offered lowercase codes
    -- Postcondition:
    --     nil, or true
    local r
    for i = 1, #accept do
        if accept[ i ] == ask then
            r = true
            break -- for i
        end
    end -- for i
    return r
end -- feasible()



local fetch = function ( access, append )
    -- Attach config or library module
    -- Precondition:
    --     access  -- module title
    --     append  -- string, with subpage part of this; or false
    -- Postcondition:
    --     Returns:  table, with library, or false
    local got, sign
    if append then
        sign = string.format( "%s/%s", access, append )
    else
        sign = access
    end
    if type( Multilingual.ext ) ~= "table" then
        Multilingual.ext = { }
    end
    got = Multilingual.ext[ sign ]
    if not got  and  got ~= false then
        local global = Multilingual.globals[ access ]
        local lib    = ( not append  or  append == "config" )
        got = foreignModule( access, lib, append, global )
        if type( got ) == "table" then
            if lib then
                local startup = got[ access ]
                if type( startup ) == "function" then
                    got = startup()
                end
            end
        else
            got = false
        end
        Multilingual.ext[ sign ] = got
    end
    return got
end -- fetch()



local fetchISO639 = function ( access )
    -- Retrieve table from commons:Data:ISO639/***.tab
    -- Precondition:
    --     access  -- string, with subpage identification
    -- Postcondition:
    --     Returns table, with data, even empty
    local r
    if type( Multilingual.iso639 ) ~= "table" then
        Multilingual.iso639 = { }
    end
    r = Multilingual.iso639[ access ]
    if type( r ) == "nil" then
        local raw = fetchData( "ISO639/" .. access )
        if type( raw ) == "table" then
            local t
            r = { }
            for i = 1, #raw do
                t = raw[ i ]
                if type( t ) == "table"  and
                   type( t[ 1 ] ) == "string"  and
                   type( t[ 2 ] ) == "string" then
                    r[ t[ 1 ] ] =  t[ 2 ]
                else
                    break -- for i
                end
            end -- for i
        else
            r = false
        end
        Multilingual.iso639[ access ] = r
    end
    return r or { }
end -- fetchISO639()



local fill = function ( access, alien, frame )
    -- Expand language name template
    -- Precondition:
    --     access  -- string, with language code
    --     alien   -- language code for which to be generated
    --     frame   -- frame, if available
    -- Postcondition:
    --     Returns string
    local template = Multilingual.tmplLang
    local r
    if type( template ) ~= "table" then
        local cnf = fetch( "Multilingual", "config" )
        if cnf then
            template = cnf.tmplLang
        end
    end
    if type( template ) == "table" then
        local source = template.title
        local f, lucky, s
        Multilingual.tmplLang = template
        if type( source ) ~= "string"  and
           type( template.namePat ) == "string"  and
           template.namePat:find( "%s", 1, true ) then
            source = string.format( template.namePat, access )
        end
        if type( source ) == "string" then
            if not Multilingual.frame then
                if frame then
                    Multilingual.frame = frame
                else
                    Multilingual.frame = mw.getCurrentFrame()
                end
            end
            f = function ( a )
                    return Multilingual.frame:expandTemplate{ title = a }
                end
            lucky, s = pcall( f, source )
            if lucky then
                r = s
            end
        end
    end
    return r
end -- fill()



local find = function ( ask, alien )
    -- Derive language code from name
    -- Precondition:
    --     ask    -- language name, downcased
    --     alien  -- language code of ask
    -- Postcondition:
    --     nil, or string
    local codes = mw.language.fetchLanguageNames( alien, "all" )
    local r
    for k, v in pairs( codes ) do
        if mw.ustring.lower( v ) == ask then
            r = k
            break -- for k, v
        end
    end -- for k, v
    if not r then
        r = Multilingual.fair( ask )
    end
    return r
end -- find()



local fold = function ( frame )
    -- Merge template and #invoke arglist
    -- Precondition:
    --     frame   -- template frame
    -- Postcondition:
    --     table, with combined arglist
    local r = { }
    local f = function ( apply )
                  if type( apply ) == "table"  and
                     type( apply.args ) == "table" then
                      for k, v in pairs( apply.args ) do
                          v = mw.text.trim( v )
                          if v ~= "" then
                              r[ tostring( k ) ] = v
                          end
                      end -- for k, v
                  end
              end -- f()
    f( frame:getParent() )
    f( frame )
    return r
end -- fold()



User.favorize = function ( accept, frame )
    -- Guess user language
    -- Precondition:
    --     accept  -- sequence table, with offered ISO 639 etc. codes
    --     frame   -- frame, if available
    -- Postcondition:
    --     Returns string with best code, or nil
    if not ( User.self or User.langs ) then
        if not User.trials then
            User.tell = mw.message.new( User.sniffer )
            if User.tell:exists() then
                User.trials = { }
                if not Multilingual.frame then
                    if frame then
                        Multilingual.frame = frame
                    else
                        Multilingual.frame = mw.getCurrentFrame()
                    end
                end
                User.sin = Multilingual.frame:callParserFunction( "int",
                                                           User.sniffer )
            else
                User.langs = true
            end
        end
        if User.sin then
            local order  = { }
            local post   = { }
            local three  = { }
            local unfold = { }
            local s, sin
            for i = 1, #accept do
                s = accept[ i ]
                if not User.trials[ s ] then
                    if #s > 2 then
                        if s:find( "-", 3, true ) then
                            table.insert( unfold, s )
                        else
                            table.insert( three, s )
                        end
                    else
                        if Multilingual.prefer[ s ] then
                            table.insert( order, s )
                        else
                            table.insert( post, s )
                        end
                    end
                end
            end -- for i
            for i = 1, #post do
                table.insert( order, post[ i ] )
            end -- for i
            for i = 1, #three do
                table.insert( order, three[ i ] )
            end -- for i
            for i = 1, #unfold do
                table.insert( order, unfold[ i ] )
            end -- for i
            for i = 1, #order do
                s = order[ i ]
                sin = User.tell:inLanguage( s ):plain()
                if sin == User.sin then
                    User.self = s
                    break -- for i
                else
                    User.trials[ s ] = true
                end
            end -- for i
        end
    end
    return User.self
end -- User.favorize()



Multilingual.fair = function ( ask )
    -- Format language specification according to RFC 5646 etc.
    -- Precondition:
    --     ask  -- string or table, as created by .getLang()
    -- Postcondition:
    --     Returns string, or false
    local s = type( ask )
    local q, r
    if s == "table" then
        q = ask
    elseif s == "string" then
        q = Multilingual.getLang( ask )
    end
    if q  and
       q.legal  and
       mw.language.isKnownLanguageTag( q.base ) then
        r = q.base
        if q.n > 1 then
            local order = { "extlang",
                            "script",
                            "region",
                            "other",
                            "extension" }
            for i = 1, #order do
                s = q[ order[ i ] ]
                if s then
                    r =  string.format( "%s-%s", r, s )
                end
            end -- for i
        end
    end
    return r or false
end -- Multilingual.fair()



Multilingual.fallback = function ( able, another )
    -- Is another language suitable as replacement?
    -- Precondition:
    --     able     -- language version specifier to be supported
    --     another  -- language specifier of a possible replacement,
    --                 or not to retrieve a fallback table
    -- Postcondition:
    --     Returns boolean, or table with fallback codes
    local r
    if type( able ) == "string"  and  #able > 0 then
        if type( another ) == "string"  and  #another > 0 then
            if able == another then
                r = true
            else
                local s = Multilingual.getBase( able )
                if s == another then
                    r = true
                else
                    local others = mw.language.getFallbacksFor( s )
                    r = feasible( another, others )
                end
            end
        else
            local s = Multilingual.getBase( able )
            if s then
                r = mw.language.getFallbacksFor( s )
                if r[ 1 ] == "en" then
                    local d = fetchISO639( "fallback" )
                    if type( d ) == "table"  and
                       type( d[ s ] ) == "string" then
                        r = mw.text.split( d[ s ], "|" )
                        table.insert( r, "en" )
                    end
                end
            end
        end
    end
    return r or false
end -- Multilingual.fallback()



Multilingual.findCode = function ( ask )
    -- Retrieve code of local (current project or English) language name
    -- Precondition:
    --     ask  -- string, with presumable language name
    --             A code itself will be identified, too.
    -- Postcondition:
    --     Returns string, or false
    local seek = mw.text.trim( ask )
    local r = false
    if #seek > 1 then
        if seek:find( "[", 1, true ) then
            local wlink = fetch( "WLink" )
            if wlink  and
               type( wlink.getPlain ) == "function" then
                seek = wlink.getPlain( seek )
            end
        end
        seek = mw.ustring.lower( seek )
        if Multilingual.isLang( seek ) then
            r = Multilingual.fair( seek )
        else
            local collection = favorites()
            for i = 1, #collection do
                r = find( seek, collection[ i ] )
                if r then
                    break -- for i
                end
            end -- for i
        end
    end
    return r
end -- Multilingual.findCode()



Multilingual.fix = function ( attempt )
    -- Fix frequently mistaken language code
    -- Precondition:
    --     attempt  -- string, with presumable language code
    -- Postcondition:
    --     Returns string with correction, or false if no problem known
    local r = fetchISO639( "correction" )[ attempt:lower() ]
    return r or false
end -- Multilingual.fix()



Multilingual.format = function ( apply, alien, alter, active, alert,
                                 frame, assembly, adjacent, ahead )
    -- Format one or more languages
    -- Precondition:
    --     apply     -- string with language list or item
    --     alien     -- language of the answer
    --                  -- nil, false, "*": native
    --                  -- "!": current project
    --                  -- "#": code, downcased, space separated
    --                  -- "-": code, mixcase, space separated
    --                  -- any valid code
    --     alter     -- capitalize, if "c"; downcase all, if "d"
    --                  capitalize first item only, if "f"
    --                  downcase every first word only, if "m"
    --     active    -- link items, if true
    --     alert     -- string with category title in case of error
    --     frame     -- if available
    --     assembly  -- string with split pattern, if list expected
    --     adjacent  -- string with list separator, else assembly
    --     ahead     -- string to prepend first element, if any
    -- Postcondition:
    --     Returns string, or false if apply empty
    local r = false
    if apply then
        local slang
        if assembly then
            local bucket = mw.text.split( apply, assembly )
            local shift = alter
            local separator
            if adjacent then
                separator = adjacent
            elseif alien == "#"  or  alien == "-" then
                separator = " "
            else
                separator = assembly
            end
            for k, v in pairs( bucket ) do
                slang = Multilingual.format( v, alien, shift, active,
                                             alert )
                if slang then
                    if r then
                        r = string.format( "%s%s%s",
                                           r, separator, slang )
                    else
                        r = slang
                        if shift == "f" then
                            shift = "d"
                        end
                    end
                end
            end -- for k, v
            if r and ahead then
                r = ahead .. r
            end
        else
            local single = mw.text.trim( apply )
            if single == "" then
                r = false
            else
                local lapsus, slot
                slang = Multilingual.findCode( single )
                if slang then
                    if alien == "-" then
                        r = slang
                    elseif alien == "#" then
                        r = slang:lower()
                    else
                        r = Multilingual.getName( slang, alien )
                        if active then
                            slot = fill( slang, false, frame )
                            if slot then
                                local wlink = fetch( "WLink" )
                                if wlink  and
                                   type( wlink.getTarget )
                                                       == "function" then
                                    slot = wlink.getTarget( slot )
                                end
                            else
                                lapsus = alert
                            end
                        end
                    end
                else
                    r = single
                    if active then
                        local title = mw.title.makeTitle( 0, single )
                        if title.exists then
                            slot = single
                        end
                    end
                    lapsus = alert
                end
                if not r then
                    r = single
                elseif alter == "c" or alter == "f" then
                    r = mw.ustring.upper( mw.ustring.sub( r, 1, 1 ) )
                        .. mw.ustring.sub( r, 2 )
                elseif alter == "d" then
                    if Multilingual.isMinusculable( slang, r ) then
                        r = mw.ustring.lower( r )
                    end
                elseif alter == "m" then
                    if Multilingual.isMinusculable( slang, r ) then
                        r = mw.ustring.lower( mw.ustring.sub( r, 1, 1 ) )
                            .. mw.ustring.sub( r, 2 )
                    end
                end
                if slot then
                    if r == slot then
                        r = string.format( "[[%s]]", r )
                    else
                        r = string.format( "[[%s|%s]]", slot, r )
                    end
                end
                if lapsus and alert then
                    r = string.format( "%s[[Category:%s]]", r, alert )
                end
            end
        end
    end
    return r
end -- Multilingual.format()



Multilingual.getBase = function ( ask )
    -- Retrieve base language from possibly combined ISO language code
    -- Precondition:
    --     ask  -- language code
    -- Postcondition:
    --     Returns string, or false
    local r
    if ask then
        local slang = ask:match( "^%s*(%a%a%a?)-?%a*%s*$" )
        if slang then
            r = slang:lower()
        else
            r = false
        end
    else
        r = false
    end
    return r
end -- Multilingual.getBase()



Multilingual.getLang = function ( ask )
    -- Retrieve components of a RFC 5646 language code
    -- Precondition:
    --     ask  -- language code with subtags
    -- Postcondition:
    --     Returns table with formatted subtags
    --             .base
    --             .region
    --             .script
    --             .suggest
    --             .year
    --             .extension
    --             .other
    --             .n
    local tags = mw.text.split( ask, "-" )
    local s    = tags[ 1 ]
    local r
    if s:match( "^%a%a%a?$" ) then
        r = { base  = s:lower(),
              legal = true,
              n     = #tags }
        for i = 2, r.n do
            s = tags[ i ]
            if #s == 2 then
                if r.region  or  not s:match( "%a%a" ) then
                    r.legal = false
                else
                    r.region = s:upper()
                end
            elseif #s == 4 then
                if s:match( "%a%a%a%a" ) then
                    r.legal = ( not r.script )
                    r.script = s:sub( 1, 1 ):upper() ..
                               s:sub( 2 ):lower()
                elseif s:match( "20%d%d" )  or
                       s:match( "1%d%d%d" ) then
                    r.legal = ( not r.year )
                    r.year = s
                else
                    r.legal = false
                end
            elseif #s == 3 then
                if r.extlang  or  not s:match( "%a%a%a" ) then
                    r.legal = false
                else
                    r.extlang = s:lower()
                end
            elseif #s == 1 then
                s = s:lower()
                if s:match( "[tux]" ) then
                    r.extension = s
                    for k = i + 1, r.n do
                        s = tags[ k ]
                        if s:match( "^%w+$" ) then
                            r.extension = string.format( "%s-%s",
                                                         r.extension, s )
                        else
                            r.legal = false
                        end
                    end -- for k
                else
                    r.legal = false
                end
                break -- for i
            else
                r.legal = ( not r.other )  and
                          s:match( "%a%a%a" )
                r.other = s:lower()
            end
            if not r.legal then
                break -- for i
            end
        end -- for i
        if r.legal then
            r.suggest = Multilingual.fix( r.base )
            if r.suggest then
                r.legal = false
            end
        end
    else
        r = { legal = false }
    end
    if not r.legal then
        local cnf = fetch( "Multilingual", "config" )
        if cnf  and  type( cnf.scream ) == "string" then
            r.scream = cnf.scream
        end
    end
    return r
end -- Multilingual.getLang()



Multilingual.getName = function ( ask, alien )
    -- Which name is assigned to this language code?
    -- Precondition:
    --     ask    -- language code
    --     alien  -- language of the answer
    --               -- nil, false, "*": native
    --               -- "!": current project
    --               -- any valid code
    -- Postcondition:
    --     Returns string, or false
    local r
    if ask then
        local slang   = alien
        local tLang
        if slang then
            if slang == "*" then
                slang = Multilingual.fair( ask )
            elseif slang == "!" then
                slang = favorites()[ 1 ]
            else
                slang = Multilingual.fair( slang )
            end
        else
            slang = Multilingual.fair( ask )
        end
        if not slang then
            slang = ask or "?????"
        end
        slang = slang:lower()
        tLang = fetch( "Multilingual", "names" )
        if tLang then
            tLang = tLang[ slang ]
            if tLang then
                r = tLang[ ask ]
            end
        end
        if not r then
            if not Multilingual.ext.tMW then
                Multilingual.ext.tMW = { }
            end
            tLang = Multilingual.ext.tMW[ slang ]
            if tLang == nil then
                tLang = mw.language.fetchLanguageNames( slang )
                if tLang then
                    Multilingual.ext.tMW[ slang ] = tLang
                else
                    Multilingual.ext.tMW[ slang ] = false
                end
            end
            if tLang then
                r = tLang[ ask ]
            end
        end
        if not r then
            r = mw.language.fetchLanguageName( ask:lower(), slang )
            if r == "" then
                r = false
            end
        end
    else
        r = false
    end
    return r
end -- Multilingual.getName()



Multilingual.i18n = function ( available, alt, frame )
    -- Select translatable message
    -- Precondition:
    --     available  -- table, with mapping language code ./. text
    --     alt        -- string|nil|false, with fallback text
    --     frame      -- frame, if available
    --     Returns
    --         1. string|nil|false, with selected message
    --         2. string|nil|false, with language code
    local r1, r2
    if type( available ) == "table" then
        local codes = { }
        local trsl  = { }
        local slang
        for k, v in pairs( available ) do
            if type( k ) == "string"  and
               type( v ) == "string" then
                slang = mw.text.trim( k:lower() )
                table.insert( codes, slang )
                trsl[ slang ] = v
            end
        end -- for k, v
        slang = Multilingual.userLang( codes, frame )
        if slang  and  trsl[ slang ] then
            r1 = mw.text.trim( trsl[ slang ] )
            if r1 == "" then
                r1 = false
            else
                r2 = slang
            end
        end
    end
    if not r1  and  type( alt ) == "string" then
        r1 = mw.text.trim( alt )
        if r1 == "" then
            r1 = false
        end
    end
    return r1, r2
end -- Multilingual.i18n()



Multilingual.int = function ( access, alien, apply )
    -- Translated system message
    -- Precondition:
    --     access  -- message ID
    --     alien   -- language code
    --     apply   -- nil, or sequence table with parameters $1, $2, ...
    -- Postcondition:
    --     Returns string, or false
    local o = mw.message.new( access )
    local r
    if o:exists() then
        if type( alien ) == "string" then
            o:inLanguage( alien:lower() )
        end
        if type( apply ) == "table" then
            o:params( apply )
        end
        r = o:plain()
    end
    return r or false
end -- Multilingual.int()



Multilingual.isLang = function ( ask, additional )
    -- Could this be an ISO language code?
    -- Precondition:
    --     ask         -- language code
    --     additional  -- true, if Wiki codes like "simple" permitted
    -- Postcondition:
    --     Returns boolean
    local r, s
    if additional then
        s = ask
    else
        s = Multilingual.getBase( ask )
    end
    if s then
        r = mw.language.isKnownLanguageTag( s )
        if r then
            r = not Multilingual.fix( s )
        elseif additional then
            r = Multilingual.exotic[ s ] or false
        end
    else
        r = false
    end
    return r
end -- Multilingual.isLang()



Multilingual.isLangWiki = function ( ask )
    -- Could this be a Wiki language version?
    -- Precondition:
    --     ask  -- language version specifier
    -- Postcondition:
    --     Returns boolean
    local r
    local s = Multilingual.getBase( ask )
    if s then
        r = mw.language.isSupportedLanguage( s )  or
            Multilingual.exotic[ ask ]
    else
        r = false
    end
    return r
end -- Multilingual.isLangWiki()



Multilingual.isMinusculable = function ( ask, assigned )
    -- Could this language name become downcased?
    -- Precondition:
    --     ask       -- language code, or nil
    --     assigned  -- language name, or nil
    -- Postcondition:
    --     Returns boolean
    local r = true
    if ask then
        local cnf = fetch( "Multilingual", "config" )
        if cnf then
            local s = string.format( " %s ", ask:lower() )
            if type( cnf.stopMinusculization ) == "string"
               and  cnf.stopMinusculization:find( s, 1, true ) then
                r = false
            end
            if r  and  assigned
               and  type( cnf.seekMinusculization ) == "string"
               and  cnf.seekMinusculization:find( s, 1, true )
               and  type( cnf.scanMinusculization ) == "string" then
                local scan = assigned:gsub( "[%(%)]", " " ) .. " "
                if not scan:find( cnf.scanMinusculization ) then
                    r = false
                end
            end
        end
    end
    return r
end -- Multilingual.isMinusculable()



Multilingual.isRTL = function ( ask )
    -- Check whether language is written right-to-left
    -- Precondition:
    --     ask  -- string, with language (or script) code
    -- Returns true, if right-to-left
    local r
    Multilingual.rtl = Multilingual.rtl or { }
    r = Multilingual.rtl[ ask ]
    if type( r ) ~= "boolean" then
        local bib = fetch( "ISO15924" )
        if type( bib ) == "table"  and
           type( bib.isRTL ) == "function" then
            r = bib.isRTL( ask )
        else
            r = mw.language.new( ask ):isRTL()
        end
        Multilingual.rtl[ ask ] = r
    end
    return r
end -- Multilingual.isRTL()



Multilingual.message = function ( arglist, frame )
    -- Show text in best match of user language like system message
    -- Precondition:
    --     arglist  -- template arguments
    --     frame    -- frame, if available
    -- Postcondition:
    --     Returns string with appropriate text
    local r
    if type( arglist ) == "table" then
        local t = { }
        local m, p, save
        for k, v in pairs( arglist ) do
            if type( k ) == "string"  and
               type( v ) == "string" then
                v = mw.text.trim( v )
                if v ~= "" then
                    if k:match( "^%l%l" ) then
                        t[ k ] = v
                    elseif k:match( "^%$%d$" )  and  k ~= "$0" then
                        p = p or { }
                        k = tonumber( k:match( "^%$(%d)$" ) )
                        p[ k ] = v
                        if not m  or  k > m then
                            m = k
                        end
                    end
                end
            end
        end -- for k, v
        if type( arglist[ "-" ] ) == "string" then
            save = arglist[ arglist[ "-" ] ]
        end
        r = Multilingual.i18n( t, save, frame )
        if p  and  r  and  r:find( "$", 1, true ) then
            t = { }
            for i = 1, m do
                t[ i ] = p[ i ]  or  ""
            end -- for i
            r = mw.message.newRawMessage( r, t ):plain()
        end
    end
    return r  or  ""
end -- Multilingual.message()



Multilingual.sitelink = function ( all, frame )
    -- Make link at local or other site with optimal linktext translation
    -- Precondition:
    --     all    -- string or table or number, item ID or entity
    --     frame  -- frame, if available
    -- Postcondition:
    --     Returns string with any helpful internal link, or plain text
    local s = type( all )
    local object, r
    if s == "table" then
        object = all
    elseif s == "string" then
        object = mw.wikibase.getEntity( all )
    elseif s == "number" then
        object = mw.wikibase.getEntity( string.format( "Q%d", all ) )
    end
    if type( object ) == "table" then
        local collection = object.sitelinks
        local entry
        s = false
        if type( collection ) == "table" then
            Multilingual.site = Multilingual.site  or
                                mw.wikibase.getGlobalSiteId()
            entry = collection[ Multilingual.site ]
            if entry then
                s = ":" .. entry.title
            elseif collection.enwiki then
                s = "w:en:" .. collection.enwiki.title
            end
        end
        r = Multilingual.wikibase( object, "labels", frame )
        if s then
            if s == ":" .. r then
                r = string.format( "[[%s]]", s )
            else
                r = string.format( "[[%s|%s]]", s, r )
            end
        end
    end
    return r  or  ""
end -- Multilingual.sitelink()



Multilingual.tabData = function ( access, at, alt, frame )
    -- Retrieve translated keyword from commons:Data:****.tab
    -- Precondition:
    --     access  -- string, with page identification on Commons
    --     at      -- string, with keyword
    --     alt     -- string|nil|false, with fallback text
    --     frame   -- frame, if available
    --     Returns
    --         1. string|nil|false, with selected message
    --         2. language code, or "error"
    local data = fetchData( access )
    local r1, r2
    if  type( data ) == "table" then
        if type( at ) == "string" then
            local seek = mw.text.trim( at )
            if seek == "" then
                r1 = "EMPTY Multilingual.tabData key"
            else
                local e, poly
                for i = 1, #data do
                    e = data[ i ]
                    if type( e ) == "table" then
                        if e[ 1 ] == seek then
                            if type( e[ 2 ] ) == "table" then
                                poly = e[ 2 ]
                            else
                                r1 = "INVALID Multilingual.tabData bad #"
                                                         .. tostring( i )
                            end
                            break   -- for i
                        end
                    else
                        break   -- for i
                    end
                end   -- for i
                if poly then
                    data = poly
                else
                    r1 = "UNKNOWN Multilingual.tabData key: " .. seek
                end
            end
        else
            r1 = "INVALID Multilingual.tabData key"
        end
    else
        r1 = data
    end
    if r1 then
        r2 = "error"
    elseif data then
        r1, r2 = Multilingual.i18n( data, alt, frame )
        r2 = r2 or "error"
    end
    return r1, r2
end -- Multilingual.tabData()



Multilingual.userLang = function ( accept, frame )
    -- Try to support user language by application
    -- Precondition:
    --     accept  -- string or table
    --                space separated list of available ISO 639 codes
    --                Default: project language, or English
    --     frame   -- frame, if available
    -- Postcondition:
    --     Returns string with appropriate code
    local s = type( accept )
    local codes, r, slang
    if s == "string" then
        codes = mw.text.split( accept:lower(), "%s+" )
    elseif s == "table" then
        codes = { }
        for i = 1, #accept do
            s = accept[ i ]
            if type( s ) == "string"  and
               s ~= "" then
                table.insert( codes, s:lower() )
            end
        end -- for i
    end
    slang = User.favorize( codes, frame )
    if slang then
        if feasible( slang, codes ) then
            r = slang
        elseif slang:find( "-", 1, true ) then
            slang = Multilingual.getBase( slang )
            if feasible( slang, codes ) then
                r = slang
            end
        end
        if not r then
            local others = mw.language.getFallbacksFor( slang )
            for i = 1, #others do
                slang = others[ i ]
                if feasible( slang, codes ) then
                    r = slang
                    break -- for i
                end
            end -- for i
        end
    end
    if not r then
        local back = favorites()
        for i = 1, #back do
            slang = back[ i ]
            if feasible( slang, codes ) then
                r = slang
                break -- for i
            end
        end -- for i
        if not r  and  codes[ 1 ] then
            r = codes[ 1 ]
        end
    end
    return r  or  favorites()[ 1 ]
end -- Multilingual.userLang()



Multilingual.userLangCode = function ()
    -- Guess a user language code
    -- Postcondition:
    --     Returns code of current best guess
    return User.self  or  favorites()[ 1 ]
end -- Multilingual.userLangCode()



Multilingual.wikibase = function ( all, about, attempt, frame )
    -- Optimal translation of wikibase component
    -- Precondition:
    --     all      -- string or table, object ID or entity
    --     about    -- boolean, true "descriptions" or false "labels"
    --     attempt  -- string or not, code of preferred language
    --     frame    -- frame, if available
    -- Postcondition:
    --     Returns
    --         1. string, with selected message
    --         2. string, with language code, or not
    local s = type( all )
    local object, r, r2
    if s == "table" then
        object = all
    elseif s == "string" then
        object = mw.wikibase.getEntity( all )
    end
    if type( object ) == "table" then
        if about  and  about ~= "labels" then
            s = "descriptions"
        else
            s = "labels"
        end
        object = object[ s ]
        if type( object ) == "table" then
            if object[ attempt ] then
                r  = object[ attempt ].value
                r2 = attempt
            else
                local poly
                for k, v in pairs( object ) do
                    poly = poly or { }
                    poly[ k ] = v.value
                end -- for k, v
                if poly then
                    r, r2 = Multilingual.i18n( poly, nil, frame )
                end
            end
        end
    end
    return r  or  "",   r2
end -- Multilingual.wikibase()



Failsafe.failsafe = function ( atleast )
    -- Retrieve versioning and check for compliance
    -- Precondition:
    --     atleast  -- string, with required version
    --                         or wikidata|item|~|@ or false
    -- Postcondition:
    --     Returns  string  -- with queried version/item, also if problem
    --              false   -- if appropriate
    -- 2020-08-17
    local since = atleast
    local last    = ( since == "~" )
    local linked  = ( since == "@" )
    local link    = ( since == "item" )
    local r
    if last  or  link  or  linked  or  since == "wikidata" then
        local item = Failsafe.item
        since = false
        if type( item ) == "number"  and  item > 0 then
            local suited = string.format( "Q%d", item )
            if link then
                r = suited
            else
                local entity = mw.wikibase.getEntity( suited )
                if type( entity ) == "table" then
                    local seek = Failsafe.serialProperty or "P348"
                    local vsn  = entity:formatPropertyValues( seek )
                    if type( vsn ) == "table"  and
                       type( vsn.value ) == "string"  and
                       vsn.value ~= "" then
                        if last  and  vsn.value == Failsafe.serial then
                            r = false
                        elseif linked then
                            if mw.title.getCurrentTitle().prefixedText
                               ==  mw.wikibase.getSitelink( suited ) then
                                r = false
                            else
                                r = suited
                            end
                        else
                            r = vsn.value
                        end
                    end
                end
            end
        end
    end
    if type( r ) == "nil" then
        if not since  or  since <= Failsafe.serial then
            r = Failsafe.serial
        else
            r = false
        end
    end
    return r
end -- Failsafe.failsafe()



-- Export
local p = { }



p.fair = function ( frame )
    -- Format language code
    --     1  -- language code
    local s = mw.text.trim( frame.args[ 1 ]  or  "" )
    return Multilingual.fair( s )  or  ""
end -- p.fair



p.fallback = function ( frame )
    -- Is another language suitable as replacement?
    --     1  -- language version specifier to be supported
    --     2  -- language specifier of a possible replacement
    local s1 = mw.text.trim( frame.args[ 1 ]  or  "" )
    local s2 = mw.text.trim( frame.args[ 2 ]  or  "" )
    local r  = Multilingual.fallback( s1, s2 )
    if type( r ) == "table" then
        r = r[ 1 ]
    else
        r = r  and  "1"   or   ""
    end
    return r
end -- p.fallback



p.findCode = function ( frame )
    -- Retrieve language code from language name
    --     1  -- name in current project language
    local s = mw.text.trim( frame.args[ 1 ]  or  "" )
    return Multilingual.findCode( s )  or  ""
end -- p.findCode



p.fix = function ( frame )
    local r = frame.args[ 1 ]
    if r then
        r = Multilingual.fix( mw.text.trim( r ) )
    end
    return r or ""
end -- p.fix



p.format = function ( frame )
    -- Format one or more languages
    --     1          -- language list or item
    --     slang      -- language of the answer, if not native
    --                   * -- native
    --                   ! -- current project
    --                   any valid code
    --     shift      -- capitalize, if "c"; downcase, if "d"
    --                   capitalize first item only, if "f"
    --     link       -- 1 -- link items
    --     scream     -- category title in case of error
    --     split      -- split pattern, if list expected
    --     separator  -- list separator, else split
    --     start      -- prepend first element, if any
    local r
    local link
    if frame.args.link == "1" then
        link = true
    end
    r = Multilingual.format( frame.args[ 1 ],
                             frame.args.slang,
                             frame.args.shift,
                             link,
                             frame.args.scream,
                             frame,
                             frame.args.split,
                             frame.args.separator,
                             frame.args.start )
    return r or ""
end -- p.format



p.getBase = function ( frame )
    -- Retrieve base language from possibly combined ISO language code
    --     1  -- code
    local s = mw.text.trim( frame.args[ 1 ]  or  "" )
    return Multilingual.getBase( s )  or  ""
end -- p.getBase



p.getName = function ( frame )
    -- Retrieve language name from ISO language code
    --     1  -- code
    --     2  -- language to be used for the answer, if not native
    --           ! -- current project
    --           * -- native
    --           any valid code
    local s     = mw.text.trim( frame.args[ 1 ]  or  "" )
    local slang = frame.args[ 2 ]
    local r
    Multilingual.frame = frame
    if slang then
        slang = mw.text.trim( slang )
    end
    r = Multilingual.getName( s, slang )
    return r or ""
end -- p.getName



p.int = function ( frame )
    -- Translated system message
    --     1             -- message ID
    --     lang          -- language code
    --     $1, $2, ...   -- parameters
    local sysMsg = frame.args[ 1 ]
    local r
    if sysMsg then
        sysMsg = mw.text.trim( sysMsg )
        if sysMsg ~= "" then
            local n     = 0
            local slang = frame.args.lang
            local i, params, s
            if slang == "" then
                slang = false
            end
            for k, v in pairs( frame.args ) do
                if type( k ) == "string" then
                    s = k:match( "^%$(%d+)$" )
                    if s then
                        i = tonumber( s )
                        if i > n then
                            n = i
                        end
                    end
                end
            end -- for k, v
            if n > 0 then
                local s
                params = { }
                for i = 1, n do
                    s = frame.args[ "$" .. tostring( i ) ]  or  ""
                    table.insert( params, s )
                end -- for i
            end
            r = Multilingual.int( sysMsg, slang, params )
        end
    end
    return r or ""
end -- p.int



p.isLang = function ( frame )
    -- Could this be an ISO language code?
    --     1  -- code
    local s = mw.text.trim( frame.args[ 1 ]  or  "" )
    local lucky, r = pcall( Multilingual.isLang, s )
    return r and "1" or ""
end -- p.isLang



p.isLangWiki = function ( frame )
    -- Could this be a Wiki language version?
    --     1  -- code
    -- Returns non-empty, if possibly language version
    local s = mw.text.trim( frame.args[ 1 ]  or  "" )
    local lucky, r = pcall( Multilingual.isLangWiki, s )
    return r and "1" or ""
end -- p.isLangWiki



p.isRTL = function ( frame )
    -- Check whether language is written right-to-left
    --     1  -- string, with language code
    -- Returns non-empty, if right-to-left
    local s = mw.text.trim( frame.args[ 1 ]  or  "" )
    return Multilingual.isRTL( s ) and "1" or ""
end -- p.isRTL()



p.message = function ( frame )
    -- Translation of text element
    return Multilingual.message( fold( frame ), frame )
end -- p.message



p.sitelink = function ( frame )
    -- Make link at local or other site with optimal linktext translation
    --     1  -- item ID
    local s = mw.text.trim( frame.args[ 1 ]  or  "" )
    local r
    if s:match( "^%d+$") then
        r = tonumber( s )
    elseif s:match( "^Q%d+$") then
        r = s
    end
    if r then
        r = Multilingual.sitelink( r, frame )
    end
    return r or s
end -- p.sitelink



p.tabData = function ( frame )
    -- Retrieve best message text from Commons Data
    --     1    -- page identification on Commons
    --     2    -- keyword
    --     alt  -- fallback text
    local suite = frame.args[ 1 ]
    local seek  = frame.args[ 2 ]
    local salt  = frame.args.alt
    local r     = Multilingual.tabData( suite, seek, salt, frame )
    return r
end -- p.tabData



p.userLang = function ( frame )
    -- Which language does the current user prefer?
    --     1  -- space separated list of available ISO 639 codes
    local s = mw.text.trim( frame.args[ 1 ]  or  "" )
    return Multilingual.userLang( s, frame )
end -- p.userLang



p.wikibase = function ( frame )
    -- Optimal translation of wikibase component
    --     1  -- object ID
    --     2  -- 1 for "descriptions", 0 for "labels".
    --           or either "descriptions" or "labels"
    local r
    local s = mw.text.trim( frame.args[ 1 ]  or  "" )
    if s ~= "" then
        local s2    = mw.text.trim( frame.args[ 2 ]  or  "0" )
        local slang = mw.text.trim( frame.args.lang  or  "" )
        local large = ( s2 ~= ""  and  s2 ~= "0" )
        if slang == "" then
            slang = false
        end
        r = Multilingual.wikibase( s, large, slang, frame )
    end
    return r or ""
end -- p.wikibase



p.failsafe = function ( frame )
    -- Versioning interface
    local s = type( frame )
    local since
    if s == "table" then
        since = frame.args[ 1 ]
    elseif s == "string" then
        since = frame
    end
    if since then
        since = mw.text.trim( since )
        if since == "" then
            since = false
        end
    end
    return Failsafe.failsafe( since )  or  ""
end -- p.failsafe()



p.Multilingual = function ()
    return Multilingual
end -- p.Multilingual

return p