The most common and most likely answer to this crossword clue is the 4 letter word ANDR
A
N
D
R
Buddy explains!
The straight part
We know that "A ‘monsieur’ (not English) read in translation" is the straight/definition part of the clue. The straight part is often a synonym or definition, in this case a ‘monsieur’ (not english) read in translation = andr.The cryptic/wordplay part
In cryptic crossword there's often an wordplay/cryptic part as well.This part involves a more complex hint, such as an anagram, homophone, hidden word, etc.
Sadly, We don't have an explanation for this specific crossword clue yet.