Is there a phrase in English "they speak one language" (or "they speak the same language") referring to "they understand each other"?
speak one language
"He's speaking my language" can be used in a metaphorical manner meaning not merely that he is speaking the same language as me, but that he is talking about my area of interest.
Another Guest wrote: can be used in a metaphorical manner
If there is no context provided, the text can be used in any manner and mostly without any true meaning.
If there is no context provided, the text can be used in any manner and mostly without any true meaning.
It's a perfectly sound phrase, if you say 'They're all speaking the same language'.