Inside of the template for "lc-row" [1], used on the page Requests for new languages [2], I've added the type of official status "Verification ongoing" which would be invoked by typing "doing" into the "status" field.
I think it's pretty plain and useful for both ourselves and those waiting for our decision. It should cover the period from adding a proposal for discussion and final decision. If there is no final decision, it should be rolled back into "discussion" status.
[1] https://meta.wikimedia.org/wiki/Template:Lc-row [2] https://meta.wikimedia.org/wiki/Requests_for_new_languages