If anyone know how to extract it dynamically then feel free to give me a tip or improve it before merging it in.
# The subtitles are defined in the manifest_url like this:
# # SUBTITLES groups
# #EXT-X-MEDIA:TYPE=SUBTITLES,GROUP-ID="textstream",NAME="Swedish",LANGUAGE="sv",AUTOSELECT=YES,DEFAULT=YES,URI="bmetgl4z0mr(12579349_ISMUSP)-textstream_swe=3000.m3u8"
# but I don't know yet how to extract it dynamically from there so they are hardcoded as a start.