Are questions about terms like "RSVP" on-topic?

Question

Technically, RSVP is a French term, or to be more exact, an abbreviation for repondez vous s'il vous plait. It seems to have found its way into the English language as a fairly common term.

Are questions about it on topic?
What about other terms with foreign origin such as faux pas or savoir faire? Where does one draw the line?

A day after asking the original, I saw this question about "alpha" and "omega," that was closed:

Are alpha and omega common abbreviations for birth and death?

The (original) Greek term is occasionally used to refer to "beginning and end." It was used in the above context to refer to "birth and death." That's not exactly a common English usage, so it a bit of a stretch, but is understandable from the Greek usage.

Is it OK if an expression is USABLE in English? Or does it have to be in "common use."

Is that going too far?

Answer 1

It's a totally appropriate question. 'RSVP' been in English use for a while (since the mid 19th c) and many English speakers probably don't even know the French it stands for.

There are lots of borrowings into English from other languages and these pose special problems for grammar and pronunciation, how should one pronounce them and how people in fact do use them, and questions about them as they pertain to English are very appropriate.

Some reference to the usage in the original language is also appropriate, but only as it can inform the (most likely) inequivalent usage in English.

Answer 2

Generally, these type of questions should be OK, so long as they directly pertain to the use of the phrase in English. If your question is about the phrase's etymology or such and does not directly pertain to English, then it would probably be better on the French Stack Exchange (assuming French phrases.

Answer 3

EL&U has the tag loan-words, so yes.

Incidentally, the Japanese Stack exchange has wasei-eigo ("English made in Japan") and loanwords as tags.