WikiLearn course translations happen through Metawiki
Report received from @Supaplex. Quoting pertinent portions of the email:
Metawiki only enables zh translation, zh-tw, or zh-cn is not available and forced to translate in zh only. This setting will work on meta because meta has added and enabled a zh conversion tool to deal with the simplified Chinese and traditional Chinese display for Chinese and Taiwanese access.
However, If we use Metawiki as a translation tools, this will make the localization of zh-cn, zh-tw not possible due to Metawiki settings for translation.
One solution is to make a special privilege of zh-tw translation on meta for WikiLearn, enable the zh-hant and zh-hans translation options for the WikiLearn UI
Another optional is to enable zh conversion mode on WikiLearn, which I doubled due to WIkiLearn is no a MediaWiki website. Or use translatewiki which separated zh-hans and zh-hant translation, or a special PO file of zh-hant to deal with zh-hant translation
If the translation issues are fixed, I am also looking forward to localizing the WikiLearn content to Taiwanesse Mandarin. So I cc some other Wikimedia Taiwan staff and member
We're planning to enable message bundle translations to Chinese variants on Metawiki by modifying the related configuration.