Module:Fallback
local p = {}
 
 function p.fblist(lang, langonly) -- list the full fallback chain from a language to en
 	local fbtable = mw.language.getFallbacksFor(lang)
 	table.insert(fbtable, 1, lang)
 	if not langonly then
 		table.insert(fbtable, 'message')
 		table.insert(fbtable, 'default')
 	end
 	return fbtable
 end
 
 function p._langSwitch(args, lang) -- args: table of translations
 	-- Return error if there is not default and no English version
 	-- otherwise returns the message in the most appropriate, plus the lang code as a second value
 	if not args.en and not args.default and not args.message and args.nocat ~= '1' then
 		return error(&quot;langSwitch error: no default&quot;)
 	end
 	-- get language (either stated one or user's default language)
 	if not lang then
 		return '&lt;strong class=&quot;error&quot;&gt;LangSwitch Error: no lang&lt;/strong&gt;' -- must become proper error
 	end
 	-- get the list of acceptable language (lang + those in lang's fallback chain) and check their content
 	for i, j in ipairs(p.fblist(lang)) do
 		if args[j] then
 			if args[j] == '~' then return nil, j end
 			if j == 'message' then return tostring(mw.message.new(args[j]):inLanguage(lang)) end -- if this is an interface message
 			if args[j] ~= '' then return args[j], j end
 		end
 	end
 	return nil
 end
 
 function p.langSwitch(frame) -- version to be used from wikitext
 	local args = frame.args
 	-- if no expected args provided than check parent template/module args
 	if not args.en and not args.default and not args.nocat then
 		args = frame:getParent().args
 	end
 	local lang
 	if args.lang and args.lang ~= '' then
 		lang = args.lang
 		args.lang = nil
 	else -- get user's chosen language
 		lang = frame:preprocess( &quot;{{int:lang}}&quot; )
 	end
 	local str, language = p._langSwitch(args, lang)
 	return str -- get the first value of the langSwitch, (the text) not the second (the language)
 end
 
 function p.fallbackpage(base, lang, formatting)
 	local languages = p.fblist(lang)
 	for i, lng in ipairs(languages) do
 		if mw.title.new(base .. '/' .. lng).exists then
 			if formatting == 'table' then
 				return {base .. '/' .. lng, lng} -- returns name of the page + name of the language
 			else
 				return base .. '/' .. lng -- returns only the page
 			end
 		end
 	end
 	return base
 end
 
 function p.autotranslate(frame) -- logic for [[template:Autotranslate]]
 	local args = frame.args
 	if not args.lang or args.lang == '' then
 		args.lang = frame:preprocess( &quot;{{int:lang}}&quot; )           -- get user's chosen language
 	end
 
 	-- find base page
 	local base = args.base
 	if not base or base == '' then
 		return '&lt;strong class=&quot;error&quot;&gt;Base page not provided for autotranslate&lt;/strong&gt;'
 	end
 	if string.sub(base, 2, 9) ~= 'emplate:' then
 		base = 'Template:' .. base   -- base provided without 'Template:' part
 	end
 
 	-- find base template language subpage
 	local page = p.fallbackpage(base, args.lang) --
 	if (not page and base ~= args.base) then
 		-- try the original args.base string. This case is only needed if base is not in template namespace
 		page = p.fallbackpage(args.base, args.lang)
 	end
 	if not page then
 		return string.format('&lt;strong class=&quot;error&quot;&gt;no fallback page found for autotranslate (base=[[%s]], lang=%s)&lt;/strong&gt;', args.base, args.lang)
 	end
 
 	-- repack args in a standard table
 	local newargs = {}
 	for field, value in pairs(args) do
 		if field ~= 'base' then
 			newargs[field] = value
 		end
 	end
 
 	-- Transclude {{page |....}} with template arguments the same as the ones passed to {{autotranslate}} template.
 	return frame:expandTemplate{ title = page, args = newargs }
 end
 
 function p.translate(page, key, lang) --translate data stored in a module
 	if type(page) == 'string' then -- if the requested translation table is not yet loaded
 		page = require('Module:' .. page)
 	end
 
 	local val
 	if page[key] then
 		val = page[key]
 	elseif page.keys and page.keys[key] then-- key 'keys&quot; is an index of all keys, including redirects, see [[Module:i18n/datatype]]
 		val = page.keys[key]
 	end
 	if not val then
 		return '&lt;' .. key .. '&gt;'
 	end
 	return p._langSwitch(val, lang)
 end
 
 function p.translatelua(frame)
 	local lang = frame.args.lang
 	local page = require('Module:' .. mw.text.trim(frame.args[1])) -- page should only contain a simple of translations
 	if not lang or mw.text.trim(lang) == '' then
 		lang = frame:preprocess( &quot;{{int:lang}}&quot; )
 	end
 	if frame.args[2] then
 		page = page[mw.text.trim(frame.args[2])]
 	end
 	return p._langSwitch(page, lang)
 end
 
 function p.runTests()
 	local toFallbackTest = require('Module:Fallback/tests/fallbacks')
 	local result = true
 
 	mw.log('Testing fallback chains')
 	for i, t in ipairs(toFallbackTest) do
 		local fbtbl = table.concat(p.fblist(t.initial), ', ')
 		local expected = table.concat(t.expected, ', ')
 		local ret = (fbtbl == expected)
 		mw.log(i, ret and 'passed' or 'FAILED', t.initial, (not ret) and ('FAILED\nis &gt;&gt;' .. fbtbl .. '&lt;&lt;\nbut should be &gt;&gt;' .. expected .. '&lt;&lt;\n') or '')
 		result = result and ret
 	end
 	
 	return result
 end
 
 function p.showTemplateArguments(frame)
 -- list all input arguments of the template that calls &quot;{{#invoke:Fallback|showTemplateArguments}}&quot;
 	local str = ''
 	for name, value in pairs( frame:getParent().args ) do
 		if str == '' then
 			str = string.format('%s=%s', name, value)          -- argument #1
 		else
 			str = string.format('%s, %s=%s', str, name, value) -- the rest
 		end
 	end
 	return str
 end