Name for using foreign language (especially Latin) to convey a sense of dignity and wisdom

My Petit Larousse has a section of Latin and foreign phrases (including some English ones such as at home, all right and Rule, Britannia! In vino veritas and sic transit gloria mundi are, of course, included.

Many of these Latin quotations came into common use in the days when all educated men understood at least some Latin - not necessarily to sound 'wise' or 'dignified', just because 'everyone' knew what they meant, and they expressed an idea succinctly.

Incidentally, annus horribilis was coined by Queen Elizabeth in imitation of the phrase annus mirabilis.

Many great comments, but not too many definitive answers, though I am going to accept Kate's answer since it does at least answer one of the questions. But I have been thinking about it a lot so thought I'd share my thoughts, which are mostly speculative.

1. Why did the queen say "annus horibilis" rather than "horrible year"? I think the answer to that comes from the word I used in my question: that it is an epigram. An epigram was, originally, carved stone notice in classical times which came to mean a concise wise or pithy statement. By putting it in a different language we make it stand out: it isn't just part of the flow of the prose, but a unit in itself. Perhaps in modern times we'd put it in a fancy font or put it framed on a line by itself. But that isn't possible in speech. So putting it in a different language provides a similar highlight.

2. I think it also conveys a bit of a sense of the in crowd. If you don't know what "c'est la meme chose" means you don't want to say lest you look stupid. If you do know what it means you nod along to make sure everyone knows how smart you are. It puts you in the in-crowd, and so makes you want to agree with it more. Much as an in-joke that only the in-crowd understand, is a bonding process. You'll laugh at it, even if it isn't very funny, to be part of the group.

3. In the past the educated elite would have been taught Latin and French. So it puts "in vino veritas" into the category of "what the educated elite think", which adds a certain intellectual cache. (If you study the history of Rome and how horrible and often stupid the leaders were, especially so when they were "in vino" you might revise that opinion though.)

4. Words or phrases mean more than their actual literal meaning often. "One swallow doth not a summer make" means very considerably more than what it literally says. And so these foreign phrases carry baggage beyond their literal meaning. And being foreign in nature they are less prone to grammatical modification and change than literal statements in the language, so tend to be rather immutable and easier to hang extra meaning onto.

5. These immutable phrases are useful, and useful things survive in the evolutionary process of language. If one can pluck out some Latin or French phrase that conveys your opinion, irrespective of how good your opinion is, the foreign nature of the phrase, its immutability and the other things above, make its putative wisdom very hard to challenge, no matter the how reasonable or accurate it might be.

I think this last point is notable. I think that "in vino veritas" came to the fore in the popular news when a famous actor got drunk and spewed his loathsome views to some unfortunate taxi driver. However, my experience is that drunk people aren't so much truthful as stupid and incoherent. So I'd suggest "In vino stultitia" -- "in wine is stupidity" -- would be more accurate. However, I doubt my idea is likely to go viral.