沈黙寡言を美徳とする文化もある。
Some cultures consider reticence a virtue.
無口 is a more common, everyday word for being quiet or taciturn, while 沈黙寡言 is a formal, literary yojijukugo.
寡黙 is a shorter, more common literary term for taciturnity; 沈黙寡言 is more emphatic and less frequently used.
A yojijukugo composed of 沈黙 (silence) and 寡言 (few words). The exact historical derivation is uncertain, but it follows the typical pattern of combining two two-character compounds to form a four-character idiom.