Translations of Wikibase and WikibaseClient can now be done at
translatewiki.net. For some
reason that I am unaware of, they are located with the group names Wikidata Repo and
Wikidata Client.
http://translatewiki.net/wiki/Special:Translate/ext-wikidataclient
http://translatewiki.net/wiki/Special:Translate/ext-wikidatarepo