Akademik

Глупый да малый всегда правду говорят
It is only foolish and naive people that always tell what they really think
Cf: Children and fools cannot lie (Br.). Children and fools speak the truth (Am., Br.). Children and fools tell the truth (Am.). If you want the truth, go to a child or a fool (Am.)

Русско-английский словарь пословиц и поговорок. . 2013.