The audio track limitation is on a per video basis. Meaning that for every video you upload, you can freely choose up to 5/10/unlimited languages.

The amount of maximal language tracks is limited by the amount of codes you redeemed. 1 codes enables you to upload videos with up to 5 language tracks, 2 codes up to 10 language tracks per video and 3 (and more) codes lets you upload unlimited language tracks.