English Translation
He never speaks unless spoken to.
FYI: 口をきく in Hiragana is more common than in Kanji. But just in case you may wonder how to spell きく in Kanji, it is 利く.
口を利く has several meanings: “to speak to (someone else)”; “to fix someone up with”; and “to be mouthy/trumpet”.
There are some homophone words of きく: 聞く (to listen to/hear); 聴く (to listen to/hear); 利く (to effectively function/to be beneficial); 効く (to take effective). Even many Japanese native speakers easily get confused especially with the difference between 利く and 効く. That’s probably the reason why 口を利く is more often spelled with Hiragana.