Wikipedia : Delete the languages you don't understand anyway.
If you're like me, you only know four languages, so the others in wikipedia's list are useless to you.
This stylesheet deletes them.
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Version 1.03 works on all wikimedia projects and anything else that runs on the mediawiki.
Version 1.04 bugfix: The box is now only as long as needed to fit the languages you added.
Version 1.05 bugfix of 1.04; and marginal simplification of code, using the "not()" pseudo selector. users don't need to fill in pixel values anymore.
(PS: this sheet is now one year old. :D )
Version 1.06: Using display instead of visibility. (Does not affect result.)

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@medjakov@userstyles (again): Ok, I'm using display:none now. (v1.06) Which is what is should be using , not because it's shorter, but because it removes instead of hide, which is what I'm doing.
@medjakov@userstyles: No, I wouldn't want that, So I made it in a separate sheet: http://freestyler.ws/style/9134/wikipedia-fade-out-languages fades instead of deleting.
@medjakov@userstyles: I did not know about