Q:

"French leave" in French

How to translate "French leave" into French?
I have searched for the translation on wordreference.com and Google separately but they both showed different results.
According to wordreference.com “French leave” translates to “filer à l'anglaise“, but if I consider the meaning of "leave" alone in French, it says congé. I am confused.

A:

The expression is indeed filer à l'anglaise (backed up by Wiktionnaire).
I don't think there's a specific noun for this. If I were translating something like "Where is he?" — "On French leave" I would just use the past tense: « Où est-il ? » — « Il a filé à l'anglaise. »
In general, a dictionary with a dedicated entry for an idiom should be trusted over Google Translate, in my experience. You really don't know what mélange of contexts the latter has found equivalents in, or if it even knows it should take the two words as a whole.
Also, don't worry about "leave" = congé on its own. Since "French leave" is an idiom, there's no way to guess the meaning from the parts alone. congé + français won't add up to "French leave" and it doesn't have to.

A:

First of all, French leave is not used so often nowadays according to 
https://www.collinsdictionary.com/dictionary/english/french-leave
More information may be found here
https://writingexplained.org/idiom-dictionary/french-leave
In any case according to 
https://www.linguee.com/english-french/search?source=auto&query=french+leave
a one to one translation might be

filer à la française

But a googling reveals that French people use 

filer à l'anglaise

instead. I think it has to do with the traditional (at least in the past) Franco-British rivalry.

Si en français, prendre la fuite se dit "filer à l'anglaise", en
  anglais, on utilise la réciproque en disant "to take french leave".

Filer à l'anglaise...

http://www.dixvinsblog.com/article-les-belles-expressions-de-la-langue-fran-aise-filer-a-l-anglaise-119527538.html

