MediaWiki:Mwe-timedtext-language-subtitles-for-clip/gsw

You could fix it using preposition before the language name (not the adjective). That's what was done in French: "sous-titre en français" with the preposition "en" before the language name "français" or "anglais".

Note that translated language names in the plaveholder $1 is always a noun (or substantive expression like "German language"), normally generated like with the "languagename:" parserfunction or seen in the "Other languages' navigation bar. Note all languages can use prepositions, or may need some transformation of this noun (such as mutation of initials in Centic languages, or elision or gluing with the preposition such as "de" into "d'" in French, Spanish, Italian): you need to find a formulation that avoids this issue (including the possibility of adding some punctuation.

Yes, I could fix it—if I spoke the language. Alemannic is similar enough to (Standard) German that I mostly understand it (at least such short texts), but it’s different enough that I can’t confidently speak/write it.