[reitanqild]

Please don't enforce it. The moment you have a "sufficiently large wordset" in English you'd already added a whole lot of words that are hard to spell not only for non-native speakers.

Why not try to generate semi random pronounceable passwords? There's a clear decrease in entropy but brute force cracking against all pronounceable strings less than 20 chars will still be hard. (Of course your definition of pronounceability might differ.)