In the TMF Reference Model, translation documentation is a kind of “progeny record” (this is the term used on the Instructions and Glossary tab). The TMF RM states that progeny records belong filed with their related artifact (as described by Jennifer above).
eTMF systems have various ways of dealing with progeny records, but as long as the translation documentation can be seen as related & is accessible from the primary record that was translated, you should be good.