Great work, my congratulations!
------------------------------- Some first impressions:
Changing the language does not really work, the title of the item pages remain in English.
http://www.wikidata.org/wiki/Special:RecentChanges?setlang=de -> (Unterschied | Versionen) . . Sweden (Q34); 17:48 . . (+32) . . Aplasia (Diskussion | Beiträge) (Fügte websitespezifischen [itwiki] Link hinzu: Paesi Bassi)
although http://www.wikidata.org/wiki/Q34 does list de: Schweden.
I am not sure whether this is a bug or by design?
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In German, translation of "Item" with "Datenelement" = data element seems odd, a data element is usually something much smaller and atomic. See http://de.wikipedia.org/wiki/Datenelement
Proposal: "Artikel" or "Datenobjekt"
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Change http://www.wikidata.org/ to http://wikidata.org/ ?
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I think the logo image (upper left corner) looks a bit lost, 10% larger perhaps? It is not even left aligned with the menu text below, which has ample margin
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Finally: The "Q###" will become the public face of Wikidata, whereever it is re-used. I think this "brand" should be less cryptic and use:
http://wikidata.org/wiki/WD34 or http://wikidata.org/wiki/W34
(providing a memnonic link to Wikidata) instead of current
Gregor