Controlling tags can result in crap, because you can't be sure that two words are the same..
I think it's safe to allow the chaos, the tag-recommendation tool is very usefull and people shouldn't start new tags if they don't think that they are necessary.
Tags for different languages sounds like a heap of work..
What ohloh definitely needs are GUI translations, this is really important, since not all speak english. once the project is inside ohloh, chances are high that english speaking ones will find it and tag it accordingly.
take a look at Jamendo for inspiration maybe..
Any chances that you will start a translation project real soon? I can work on a german one!
I heard bad things about launchpad.net on inkscape's irc I think btw, I think it was license-related (they require you to use cc-by 2.5? - likely to be wrong info)