I put down "Do you understand Klingon language" and it didnt accept it. Is it wrong or is it just not added to asnwers?
Maybe because your sentence is missing "the" before "Klingon language"?
"Do you understand Klingon?" is ok without "the" but your sentence is not grammatical English.
Weird thing. I can't hear pronunciation at all... Is that a bug?
Probably. Are you using Android? We know about the problems with the Android app and the programmers are working on it. However, if you couldn't hear the pronunciation on the Web or iOS app, please reply back to let me know.