Scripts are copyrighted but the translated subtitles are never straight translations of scripts (as I have found out in recent years being English in a non-English country), there is a level of interpretation (using a similar phrase, or a different cultural reference, perhaps just converting imperial to metric).

Then you have to also consider the fact that many of the subtitles included on DVDs and sometimes even theatrical releases (at least in Sweden and Norway) are very often lifted from online sources the movie companies attack (rather than them hiring actual translators for all the markets they wish to conquer).

Finally... I might be wrong on this but what happened to fair use? There were cases in the 80's that cemented our standard of fair use. Humming a song on the street is fair use, providing translated derivative works when no alternative exists is fair use.