Dmen,
It depends what you value. The GWT team values load time over all else, which makes sense given the hit volume their pages face. Simply put, they want to send each user a single permutation. The cost of storing 320 permutations on the server (i.e. 400MB) is far cheaper than packing all of that into a single permutation (i.e. 5MB vs 1MB) given the download and parse time for such a large JS wad. Even downloading a i18n file for each language to the UI is a poor idea given one more server hit and that the UI can't init unit it has words to show.
So that's the flavor of the GWT Kool-Aid.
If the build time is perturbing, just Google for distributed GWT permutation building. That's how Google teams get around that issue.
Sincerely,
Joseph