Module:Template translation
local this = {}
 
 function this.checkLanguage(subpage, default)
     --[[Check first if there's an any invalid character that would cause the
         mw.language.isKnownLanguageTag function() to throw an exception:
         - all ASCII controls in [\000-\031\127],
         - double quote (&quot;), sharp sign (#), ampersand (&amp;), apostrophe ('),
         - slash (/), colon (:), semicolon (;), lower than (&lt;), greater than (&gt;),
         - brackets and braces ([, ], {, }), pipe (|), backslash (\\)
         All other characters are accepted, including space and all non-ASCII
         characters (including \192, which is invalid in UTF-8).
     --]]
     if mw.language.isValidCode(subpage) and mw.language.isKnownLanguageTag(subpage)
     --[[However &quot;SupportedLanguages&quot; are too restrictive, as they discard many
         valid BCP47 script variants (only because MediaWiki still does not
         define automatic transliterators for them, e.g. &quot;en-dsrt&quot; or
         &quot;fr-brai&quot; for French transliteration in Braille), and country variants,
         (useful in localized data, even if they are no longer used for
         translations, such as zh-cn, also useful for legacy codes).
         We want to avoid matching subpagenames containing any uppercase letter,
         (even if they are considered valid in BCP 47, in which they are
         case-insensitive; they are not &quot;SupportedLanguages&quot; for MediaWiki, so
         they are not &quot;KnownLanguageTags&quot; for MediaWiki).
         To be more restrictive, we exclude tags
         * for specific uses in template subpages and unusable as language tags;
         * that is not ASCII and not a lowercase letter, minus-hyphen, or digit,
           or does not start by a letter or does not finish by a letter or digit;
         * or that has subtags with more than 8 characters between hyphens;
         * or that has two hyphens.
     --]]
     or  subpage ~= &quot;doc&quot;
     and subpage ~= &quot;layout&quot;
     and subpage ~= &quot;button&quot;
     and subpage ~= &quot;buttons&quot;
     and subpage ~= &quot;sandbox&quot;
     and subpage ~= &quot;testcase&quot;
     and subpage ~= &quot;testcases&quot;
     and string.find(subpage, &quot;^[%l][%-%d%l]*[%d%l]$&quot;) ~= nil
     and string.find(subpage, &quot;[%d%l][%d%l][%d%l][%d%l][%d%l][%d%l][%d%l][%d%l][%d%l]&quot;) == nil
     and string.find(subpage, &quot;%-%-&quot;) == nil then
         return subpage
     end
     -- Otherwise there's currently no known language subpage
     return default
 end
 
 --[[Get the last subpage of an arbitrary page if it is a translation.
     To be used from templates.
     ]]
 function this.getLanguageSubpage(frame)
 	local title = frame and frame.args[1]
 	if not title or title == '' then
 		title = mw.title.getCurrentTitle()
 	end
 	return this._getLanguageSubpage(title)
 end
 
 --[[Get the last subpage of an arbitrary page if it is a translation.
     To be used from Lua.
     ]]
 function this._getLanguageSubpage(title)
 	if type(title) == 'string' then
 		title = mw.title.new(title)
 	end
 	if not title then
 		-- invalid title
 		return nil
 	end
 	--[[This code does not work in all namespaces where the Translate tool works.
 	--  It works in the main namespace on Meta because it allows subpages there
 	--  It would not work in the main namespace of English Wikipedia (but the
 	--  articles are monolignual on that wiki).
 	--  On Meta-Wiki the main space uses subpages and its pages are translated.
 	--  The Translate tool allows translatng pages in all namespaces, even if
 	--  the namespace officially does not have subpages.
 	--  On Meta-Wiki the Category namespace still does not have subpages enabled,
 	--  even if they would be very useful for categorizing templates, that DO have
 	--  subpages (for documentatio and tstboxes pages). This is a misconfiguration
 	--  bug of Meta-Wiki. The work-around is to split the full title and then
 	--  get the last titlepart.
 	local subpage = title.subpageText
 	--]]
 	local titleparts = mw.text.split(title.fullText, '/')
 	local subpage = titleparts[#titleparts]
 	return this.checkLanguage(subpage, '')
 end
 
 --[[Get the last subpage of the current page if it is a translation.
     ]]
 function this.getCurrentLanguageSubpage()
 	return this._getLanguageSubpage(mw.title.getCurrentTitle())
 end
 
 --[[Get the first part of the language code of the subpage, before the '-'.
 --]]
 function this.getMainLanguageSubpage()
 	parts = mw.text.split(this.getCurrentLanguageSubpage(), '-')
 	return parts[1]
 end
 
 --[[Get the last subpage of the current frame if it is a translation.
     Not used locally.
 --]]
 function this.getFrameLanguageSubpage(frame)
 	return this._getLanguageSubpage(frame:getParent():getTitle())
 end
 
 --[[Get the language of the current page. Not used locally.
 --]]
 function this.getLanguage()
     local subpage = mw.title.getCurrentTitle().subpageText
     return this.checkLanguage(subpage, mw.language.getContentLanguage():getCode())
 end
 
 --[[Get the language of the current frame. Not used locally.
 --]]
 function this.getFrameLanguage(frame)
     local titleparts = mw.text.split(frame:getParent():getTitle(), '/')
     local subpage = titleparts[#titleparts]
     return this.checkLanguage(subpage, mw.language.getContentLanguage():getCode())
 end
 
 function this.title(namespace, basepagename, subpage)
     local message, title
     local pagename = basepagename
     if (subpage or '') ~= '' then
         pagename = pagename .. '/' .. subpage
     end
     local valid, title = xpcall(function()
             return mw.title.new(pagename, namespace) -- costly
         end, function(msg) -- catch undocumented exception (!?)
             -- thrown when namespace does not exist. The doc still
             -- says it should return a title, even in that case...
             message = msg
         end)
     if valid and title ~= nil and (title.id or 0) ~= 0 then
         return title
     end
     return { -- &quot;pseudo&quot; mw.title object with id = nil in case of error
         prefixedText = pagename, -- the only property we need below
         message = message -- only for debugging
     }
 end
 
 --[[If on a translation subpage (like Foobar/de), this function returns
     a given template in the same language, if the translation is available.
     Otherwise, the template is returned in its default language, without
     modification.
     This is aimed at replacing the current implementation of Template:TNTN.
 
     This version does not expand the returned template name: this solves the
     problem of self-recursion in TNT when translatable templates need themselves
     to transclude other translable templates (such as Tnavbar).
 --]]
 function this.getTranslatedTemplate(frame, withStatus)
     local args = frame.args
     local pagename = args['template']
     --[[Check whether the pagename is actually in the Template namespace, or
         if we're transcluding a main-namespace page.
         (added for backward compatibility of Template:TNT)
         ]]
     local namespace, title = args['tntns'] or ''
     if namespace ~= '' then -- Checks for tntns parameter for custom ns.
         title = this.title(namespace, pagename) -- Costly
     else -- Supposes that set page is in ns10.
     	namespace = 'Template'
         title = this.title(namespace, pagename) -- Costly
         if title.id == nil then -- not found in the Template namespace, assume the main namespace (for backward compatibility)
     	    namespace = ''
             title = this.title(namespace, pagename) -- Costly
         end
     end
     -- Get the last subpage and check if it matches a known language code.
     local subpage = args['uselang'] or ''
     if subpage == '' then
         subpage = this.getCurrentLanguageSubpage()
     end
     if subpage == '' then
         -- Check if a translation of the pagename exists in English
         local newtitle = this.title(namespace, pagename, 'en') -- Costly
         -- Use the translation when it exists
         if newtitle.id ~= nil then
             title = newtitle
         end
     else
         -- Check if a translation of the pagename exists in that language
         local newtitle = this.title(namespace, pagename, subpage) -- Costly
         if newtitle.id == nil then
             -- Check if a translation of the pagename exists in English
             newtitle = this.title(namespace, pagename, 'en') -- Costly
         end
         -- Use the translation when it exists
         if newtitle.id ~= nil then
             title = newtitle
         end
     end
     -- At this point the title should exist
     if withStatus then
     	-- status returned to Lua function below
         return title.prefixedText, title.id ~= nil
     else
     	-- returned directly to MediaWiki
         return title.prefixedText
     end
 end
 
 --[[If on a translation subpage (like Foobar/de), this function renders
     a given template in the same language, if the translation is available.
     Otherwise, the template is rendered in its default language, without
     modification.
     This is aimed at replacing the current implementation of Template:TNT.
     
     Note that translatable templates cannot transclude themselves other
     translatable templates, as it will recurse on TNT. Use TNTN instead
     to return only the effective template name to expand externally, with
     template parameters also provided externally.
 --]]
 function this.renderTranslatedTemplate(frame)
 	local title, found = this.getTranslatedTemplate(frame, true)
     -- At this point the title should exist prior to performing the expansion
     -- of the template, otherwise render a red link to the missing page
     -- (resolved in its assumed namespace). If we don't tet this here, a
     -- script error would be thrown. Returning a red link is consistant with
     -- MediaWiki behavior when attempting to transclude inexistant templates.
 	if not found then
 		return '[[' .. title .. ']]'
 	end
     -- Copy args pseudo-table to a proper table so we can feed it to expandTemplate.
     -- Then render the pagename.
     local args = frame.args
     local pargs = (frame:getParent() or {}).args
     local arguments = {}
     if (args['noshift'] or '') == '' then
         for k, v in pairs(pargs) do
             local n = tonumber(k) or 0
             if n &lt;= 0 then -- unnumbered args
                 arguments[k] = v
             elseif n &gt;= 2 then -- numbered args &gt;= 2 need to be shifted
                 arguments[n - 1] = v
             end
         end
     else -- special case where TNT is used as autotranslate
     	-- (don't shift again what is shifted in the invokation)
         for k, v in pairs(pargs) do
             arguments[k] = v
         end
     end
     arguments['template'] = title -- override the existing parameter of the base template name supplied with the full name of the actual template expanded
     arguments['tntns'] = nil -- discard the specified namespace override
     arguments['uselang'] = args['uselang'] -- argument forwarded into parent frame
     arguments['noshift'] = args['noshift'] -- argument forwarded into parent frame
     return frame:expandTemplate{title = ':' .. title, args = arguments}
 end
 
 --[[A helper for mocking TNT in Special:TemplateSandbox. TNT breaks
     TemplateSandbox; mocking it with this method means templates won't be
     localized but at least TemplateSandbox substitutions will work properly.
     Won't work with complex uses.
 --]]
 function this.mockTNT(frame)
     local pargs = (frame:getParent() or {}).args
     local arguments = {}
     for k, v in pairs(pargs) do
         local n = tonumber(k) or 0
         if n &lt;= 0 then -- unnumbered args
             arguments[k] = v
         elseif n &gt;= 2 then -- numbered args &gt;= 2 need to be shifted
             arguments[n - 1] = v
         end
     end
     if not pargs[1] then
     	return ''
 	end
     return frame:expandTemplate{title = 'Template:' .. pargs[1], args = arguments}
 end