VobSubMuxer can join more than one languages on one single vobsub file (idx/sub). Vobsub files, generated by the extracion of the dvd, can contain more than one language streams.
So if you rip an dvd on your computer, the extracted idx/sub package may contain more than one languages in one file[sub/idx].This is an really good solution if you want to watch your film (test.avi) with all the supported languages that where on dvd (test.sub/test.idx)