On releases with songs sung in a language other than that of the target market, it is common to find translations of the lyrics in the release's liner notes. At present the "liner notes" relationship is the closest we have for crediting the individuals responsible for these translations; there ought to be something more specific that doesn't involve adding a bogus "lyricist" or "translator" relationship at the release level.
Example:
Trish LeDoux provided lyric translation on Ranma ½ Original TV Soundtrack, Volume 1
あらい・あきら provided lyric translation on 52nd Street