@RenPythagorus
As I said, you can replace chars that are troublesome with something that isn't, and after translating you can raplece them back.
As for too large files, solution is easy. Just cut them in pieces, and after traslating put them together.(If you want, but it doesn't matter if they're separeted.)
Renpy doesn't care where are files and how are named, only if they're in tl\langname catalog.
Anyway I reccomend you to do it like I said, because files will be smaller.(Almost 2 times.) Especially since you said that size is a problem.
So if you do it with translations.txt, you can cut only this file into pieces and just apply these parts with program to your traslation files. In this way, you'll avoid creating additional files.
Your way of doing fast translation will only work if you'll check yourself everyline after traslating, and correct misspelled lines.
Because if you not, then you'll get broken traslation instead of bearable one.
And why won't I do it this way? Well, my English is bad, so I can't check and correct it quickly like some common person, especially when my basic language skill are also poor.
Thus, I'm not fitted to do this kind of work, but I'll do it anyway, in my way.