I seem to remember there being a pirush in the back of the gemara that explains the French of Rashi and translates it into German. It may be only in the fancier new prints, but I can't seem to find it. Can anyone identify this commentator?
It's called המתרגם. The reason it's hard to find is because it is not consistently printed in the same place in all masechtos. Check before and after the Maharsha, that's usually where the printers found place to squeeze it in.
The standard Vilna 'Shaar Blaat' mentions it's collation at the bottom of side two in the section ומלבד כל אלו הוספנו by number 15, it seems to be an anonymous addition from the printers.