70K on District 9 Ultimatum (mind you thats a dedicated srt file without menu links and stuff)
.srts are plaintext. Subtitles on a DVD are stored as four-colour (presumably at least RLE compressed) bitmaps. Rough guess, 2k a frame, let's say average 10 frames a minute, 120 minutes... ~2mb per language.
Im working on the Welsh language and the Backstroke of the west subs straight away ;-P
Look you now, Obi-wan, I'm the master now, see? There's lovely.
DE