Trying at add a new statement with a monolingual string datatype fails with:
jQuery.Deferred exception: LanguageSelector is not a constructor TypeError: LanguageSelector is not a constructor
Trying to edit an existing statement (example) fails with the same error.
I suspect this might be todo with the RL terminators?
Guess if that is the case we might need to revert something soon-ish. As far as I can see it isn't broken on wikidata.org
Monolingual string values cannot be edited (currently on wikidata.beta.wmflabs.org and test.wikidata.org)