"弦乐四重奏曲" can be translated into English as "string quartet" (when referring to the musical composition) or "string quartet piece" (for a more explicit emphasis on it being a piece of music).
In musical contexts, "string quartet" is widely recognized and commonly used to describe a composition written for two violins, a viola, and a cello. For example, you might say, "Beethoven wrote several famous string quartets."