I’m trying to translate a Vietnamese proverb into English, and I couldn’t find an idiom or proverb in English that provides an exact match with my Vietnamese one.
The Vietnamese one goes as follows: “bằng mặt mà không bằng lòng” (literal translation: equal face but not equal stomach/heart). It is often used to describe your relationship with someone who you are not really fond of or in fact, you despise them, but you still have to put on a face while interacting with them.
For example, you hate your boss and think that he does not deserve such a position, but since it’s a professional workplace environment and he’s still your boss, you still have to be nice to him and sometimes show that you agree (but internally you totally disagree) with his meaningless and dull opinions.
This Vietnamese expression is actually a direct translation of an old Chinese (Mandarin) proverb, which is "面和心不和" /miàn hé xīn bù hé/. They resemble each other's meaning, which is "remain friendly in appearance but estranged at heart".
In Vietnam, this is not considered a bad, sinister, or diabolical action, since it is actually considered much better to keep the situation at peace rather than stirring up unnecessary troubles arising only due to personal feelings.