The best language for subtitles, in most cases, will be English, especially for maths and science.
However, I was wondering if more than one language will be supported. At least English + the native language of the location in question?
If this is not in the pipeline I was thinking of create two instances of kolibri. One for English and one for the local language. Taking an English VTT file and translating it with Google can be 95% automated. Admittedly the translation will not be perfect but it is very much better than nothing. Proper translation would take a massive amount of time, but this way, non-native speakers of English can have local subtitles that are a little quirky, but QUICKLY.
I tried modifying a VTT file but the changes were not reflected on screen, even after restarting the server. Therefore my main question is how to get VTT changes activated in Kolibri?