It is not only in BTTF - also appears in Sam and Max. The problem is known for a year now and it is not still resolved
I've talked to a Let's Player. He does not have this problem. He had the CD version. As it seems, Steam & Co. has an outdated version of the game.
I've found in the Steam forum. This corrects all errors.
Ok, temporary solution for you guys until I can get this fixed Steam-side: Ok, open up the pack data folder of the episode in question. For example C:\Program Files\Steam\steamapps\common\sam and max episode ...x...\Pack\data
Then go down and find the file SamMax10...x..._english.ttarch and delete it. In fact, delete all of the ttarch files that aren't German just in case.
Hopefully, when you boot up the game again, it will just work without any lines being cut off. If it doesn't though, please let me know.