Board Thread:Questions and Answers/@comment-26285368-20150805211311/@comment-61022-20150810150204

Technically, Black Bolt has always been able to speak. The only problem being his voice is highly destructive.

So far as I can tell, there isn't any indication prior to Secret Wars that would indicate that Black Bolt was able to control his powers sufficiently to be able to speak and not cause destruction.

I haven't read Attilan Rising, but I would suspect that this is probably a new plot element that will be explained as the series progresses (if I'm not mistaken there have only been 2 issues released as yet) I wouldn't let yourself be confused by it unless they left it unexplained before the end of Secret Wars.