Special:AdvancedTranslate not opening up for mr language

You're not only one:
[8fadbc5f] /w/i.php?language=zh-hans&module=special&title=Special%3AAdvancedTranslate Exception from line 4186 of /www/translatewiki.net/w/languages/Language.php: Invalid language code "CODE"

Backtrace:

1. 0 /www/translatewiki.net/w/languages/Language.php(4215): Language::getFileName(string, string, string)
2. 1 /www/translatewiki.net/w/extensions/Translate/ffs/MediaWikiComplexMessages.php(611): Language::getMessagesFileName(string)
3. 2 /www/translatewiki.net/w/extensions/Translate/specials/SpecialMagic.php(167): SpecialPageAliasesCM->__construct(string)
4. 3 /www/translatewiki.net/w/includes/specialpage/SpecialPage.php(382): SpecialMagic->execute(NULL)
5. 4 /www/translatewiki.net/w/includes/specialpage/SpecialPageFactory.php(516): SpecialPage->run(NULL)
6. 5 /www/translatewiki.net/w/includes/MediaWiki.php(294): SpecialPageFactory::executePath(Title, RequestContext)
7. 6 /www/translatewiki.net/w/includes/MediaWiki.php(609): MediaWiki->performRequest()
8. 7 /www/translatewiki.net/w/includes/MediaWiki.php(458): MediaWiki->main()
9. 8 /www/translatewiki.net/w/index.php(46): MediaWiki->run()
10. 9 {main}

Translation of Extension's Special Page titles now fixed, however the "MediaWiki Core" still empty.

Nice of you, for your prompt response and keeping track of the issues. Thanks and warm regards