You could use vice versa:
I am looking for a possibly short phrase in formal language defining translation from a native language to a foreign one and from a foreign language to a native one. May I name it "two-way translations" or rather "bilingual translations"?
Certainly, the phrase translations from French to English and vice versa would work perfectly, but I don't want to specify the languages.
What do you have against bilingual translations? The two words don't work together in English?
Bilingual- doesn't imply two-way to me, so I'd use two-way.