Ngữ in “ngôn ngữ” means language Both ngôn ngữ and tiếng mean language but ngôn ngữ is a Chinese Vietnamese word.

ngữ is a sino vietnamese word that often has to go with another word like ngữ pháp, ngôn ngữ etc. tiếng is a pure vietnamese word.

Ngữ is the words, Tiếng is the sound , Nghĩa is the meaning

Well, ngữ is like Language. Tiếng is like Sound