**Feature summary** (what you would like to be able to do and where):
Support the apc language code.
**Use case(s)** (list the steps that you performed to discover that problem, and describe the actual underlying problem which you want to solve. Do not describe only a solution):
I want to be able to use `language=apc` (for instance) in citation templates on the English Wikipedia.
However, there is a limited number of supported languages for citation on Wikipedia: https://en.wikipedia.org/wiki/Template:Citation_Style_documentation/language/doc
In particular, some Arabic varieties such as apc (North Levantine) are not recognized whereas others such as arz (Egyptian), arq (Algerian), aeb (Tunisian), shu (Chadian), and ary (Moroccan) are: https://en.wikipedia.org/wiki/Help_talk:Citation_Style_1#Add_languages
**Benefits** (why should this be implemented?):
Support one of the most spoken and most widely understood Arabic varieties in the Arab world.
According to {T187344}; "If one or the other language code is needed (for labels/descriptions/aliases) or just monolingual string or lexemes, it might be worth creating a separate request.", here it is!
See also: {T286290} & {T286417}
Adding languages: https://www.mediawiki.org/wiki/Manual:Adding_and_removing_languages
[x] Add to translatewiki
[ ] Add to cldr extension if possible or the cldr overrides
[x] Add to language-data if not possible to add to cldr extension
[ ] Add to `includes/languages/data/Names.php`
[ ] Set fallback etc
[ ] Add to jquery.ime
[ ] Add to rtl languages of MF
[ ] Add to release notes
(Comment: The initial version of this task included the ajp code, but that code was deprecated in ISO 639 since then.)