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 ("), sharp sign (#), ampersand (&), apostrophe ('),
- slash (/), colon (:), semicolon (;), lower than (<), greater than (>),
- 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 "SupportedLanguages" are too restrictive, as they discard many
valid BCP47 script variants (only because MediaWiki still does not
define automatic transliterators for them, e.g. "en-dsrt" or
"fr-brai" 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 "SupportedLanguages" for MediaWiki, so
they are not "KnownLanguageTags" 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 ~= "doc"
and subpage ~= "layout"
and subpage ~= "button"
and subpage ~= "buttons"
and subpage ~= "sandbox"
and subpage ~= "testcase"
and subpage ~= "testcases"
and string.find(subpage, "^[%l][%-%d%l]*[%d%l]$") ~= nil
and string.find(subpage, "[%d%l][%d%l][%d%l][%d%l][%d%l][%d%l][%d%l][%d%l][%d%l]") == nil
and string.find(subpage, "%-%-") == 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
local title = and .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 if it is a translation.
Not used locally.
---
function this.getFrameLanguageSubpage
return this._getLanguageSubpage(: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 . Not used locally.
---
function this.getFrameLanguage
local titleparts = mw.text.split(: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 { -- "pseudo" 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(, withStatus)
local args = .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