This user-provided translations mechanism in VDH is very new and this is my first feedback:
I asked in the general support forum people to submit contributions to a dedicated forum and so far i’m rather satisfied: i get locale updates for German, Spanish, Dutch and Italian, plus 2 new locales Upper/Lower Sorbian (local German dialects). At some point, i will advertise more about the feature and the way to share directly within the add-on, so more people are likely to contribute.
About weh translation being ugly : well, yes, that’s not where the time was spent in priority. I’ll improve this when it will become the worst part of the add-on. Or maybe someone else will have done do (weh is open-source).
But, my strong feeling about this is that an equivalent mechanism should be implemented directly in Firefox. So no need for weh to support the feature. You can follow the related bugzilla bug about this and maybe write there you would like this feature.