That would be fantastic. I know [user]weks[/user] was doing a language pack for French, I'm not sure how far it ever got though as he's also essentially "all" our styling team.
Hopefully it will be finished by the next release. By that time we'll have a dedicated section on our website up and running to handle language pack uploads.
Unfortunately there is no official diff facility yet, this will be done in the re-design of our website, which should be happening shortly. It will point out exactly which lines in all the language files have changed though, without needing to upload anything and just by selecting the version to compare to/from.
That is the current plan, but it will definitely be very easy to compare language packs when added - however it is done in the end.
chris [at] get-aura [dot] org