I don't know about 'in medias res', and I haven't heard anyone say it, but an English friend of mine sometimes uses the expression 'quid pro quo'. I keep looking it up, and keep forgetting the meaning of it! :-)

@Katharina
Thanks for your reply.
To my opinion "quid pro quo" is more than just a phrase. I know it as an economical principle. I think these are two different things?!

Hi Betty Boo,
"e.g." is no deviation from the original Latin, it just stays for "exempli gratia" (approximately "for the pleasure of the example") but everyone nowadays reads it correctly as "for example".
About the use of Latin phrases in English, I've seldom heard them really embossed in the sentence: more often they are inserted as if within quotes (the movie began, so to speak, "in medias res" / let's restart "ab ovo". Easy in writing, less easy while speaking: pronouncing the quotes without gesturing is nearly an art :-)

There are still a few exceptions to the above, as for instance "P.S." ("post scriptum") and "a priori", that have been fully adopted and are used as a legitimate part of current English. Be tolerant: where would English be without its countless exceptions?

Does it answer your question?

@Katharina
"quid pro quo" literally means "something in exchange for something else"; in simpler and direct words, "not for free".

@Sherlock

YES! Thank you very much!

Nice weekend to all!

The following spring to mind and are all commonly used. There are also many latin terms used in legal jargon and also medical jargon. I remember the "quid pro quo" thing, which was in Silence of the Lambs. I know nothing about, Latin, however!
ad hoc, ad infinitum, ad nauseam
annus horribilis - the Queen used that one in one of her Xmas speeches!
Carpe diem
pro rata
status quo
nota bene (n.b.)
per capita
vice versa
sic
nil desperandum
post scriptum (p.s.)
per annum (p.a.)
mea culpa
versus
ipso facto
modus operandi
per se
quod erat demonstrandum (QED)
bona fide
in flagrante
persona non grate
ex gratia
in vitro (fertilisation)
in loco parentis
exeat (usually used for boarding school children having leave)
circa
in absentia
et cetera
de facto
coitus interruptus!!!
Compos mentis
id est (i.e.)

@ Sherlock, yes I think that's it. I don't recall the context in which I've heard my friend use it, but you're probably right.

@ Debs: blimey! You seem to have a lot of time on your hands ;-)

Debs,
if you start counting the Latin expressions used in medical, juridical and more generally scientific lingos, you're likely to be finished by next Easter :-)
I think that it would be wise to separate the expressions employed by scholars and cultivated people from the ones currently used by the man in the street without a clear notion about their origins and real meanings.
Among the latter I would count (quoting from your post) "vice versa", "post scriptum", "circa", "et coetera", "id est", "versus" and, of course, "coitus interruptus". And perhaps, with some perplexity, "pro capite", "compos sui", "mea culpa" and "modus operandi".
The rest is seldom heard in the underground, is it?

Let me just mention a juicy Latin quotation I heard somewhere, sounding more or less "still better than the 'praesentia spiritus' is the 'absentia corporis', believe me" -- a notably polite and elegant way of saying "beat it" :)

It seems more acceptable in BE than in AE to use Latin expressions outside of scholarly publications.

What about a.m. (ante meridiem) & p.m. (post meridiem)?

Was man in wissenschaftlichen Texten oft liest, wenn jemand einen falschen Schluss aus irgendwelchen Annahmen zieht ist folgendes:
This is a non sequitur.

Oder auch immer wunderschön in diesem Zusammenhang: sine qua non - von lateinisch "conditio sine qua non", was ohne das "conditio" eigentlich wenig Sinn ergibt.

Although many Latin phrases are used in (British) English, I don't think "in medias res" is at all common nowadays (definitely a lot less common than in German IMO). "A priori" sounds quite normal to me.

To answer the question "Would you say: "Let's got in medias res"?

No.

Although I am quite happy using phrases like "ceteris paribus" and "non sequitur", I would not use "in medias res" and I don't think I've ever heard it in England (though it is in the OED).

Depending on the precise meaning in context, one might say something like:
"Let's get straight to the point"
"Shall we skip the preliminaries?"
"Let's get down to brass tacks" (probably BE rhyming slang)
"Let's get down to the nitty gritty" (possibly avoided by people who also avoid words like "niggardly").

English-speaking doctors used to write prescriptions in Latin (as if the patients didn't have enough trouble with their handwriting!) and often this was typed onto the label of the medicine prepared - much to the confusion of patients who didn't know (or remember) any Latin.

My father used to tell the story about a patient given a medicine which said on the label: "To be taken 'in recumbent posturat"'. The patient went back to the chemist's to ask if they had any "recumbent posturat" so that he could take his medicine. The pharmacist himself wasn't there, so he asked the assistant. "Sorry," she replied, "we're out of that at the moment. Please come back on Monday!"

@Sherlock: It wouldn't be correct Latin to asy, "The movie began, so to speak, 'in medias res"'. "In medias res" is the accusative and denotes direction; you can "go" 'in medias res', but you would have to "start" 'in mediis rebus' (or better: 'mediis in rebus'), since the ablative denotes the 'place'.

"inter alia" is one that frequently pops up in patent translations. There are quite a few more.

@Reinhard W.
Of course, by the book: the accusative doubtlessly denotes a 'motus ad locum'. Yet apparently over the centuries the common use turned it into a 'status in loco' and today it is very seldom to hear expressions such as "he jumped 'in medias res"' whereas it is fainly more common to find the idiom meant as a sort of starting point. It is not the only occurrence where the use prevailed over the grammar - consider that most Latin quotations reached us through priests and monks that by necessity weren't always scholars.

An excerpt from Bryan Garner, who has also written on legal English:

LATINISMS. In the English language, Latin words and phrases typically fall into any of six categories: (1) the ones that are now so common that they're barely recognizable as Latin (bonus, quorum, vice versa); (2) the ones that are reduced to abbreviations in scholarly contexts (e.g., i.e., ibid., id.); (3) the ones used in jargon of doctors, lawyers, and scientists (metatarsus, habeas corpus, chlorella); (4) the mottoes and maxims used especially in ceremonial contexts (E pluribus unum, Sic transit gloria mundi); (5) the ones that literate people know and occasionally find useful (ipse dixit, non sequitur, rebus, mutatis mutandis); and (6) the truly rare ones that characterize SESQUIPEDALIA (ceteris paribus, hic et ubique, ignoratio elenchi). Increasingly, the view among stylists today is that unless you know that your audience is fairly erudite, categories 3 through 6 are dangerous territory.
—Garner, Dict. of Mod. Amer. Usage, 1998, p. 400

I would certainly agree at least that (6) is dangerous territory for the increasingly many of us who never took Latin. That is, I had never heard of Mike E.'s 'ceteris paribus' at all, or Sherlock's 'pro capite' and 'compos sui.' AFAIK 'exeat' is BE, though 'exit' and 'exeunt' appear in older stage directions. 'Ab ovo' and 'nil desperandum' I would also class as relatively uncommon, passive but not active vocabulary. But most of the rest mentioned so far, like 'persona non grata' (the correct spelling) and the rest of Debs's helpful list, are indeed very common.

One note, though: Be sure to distinguish between abbreviations, many of which are widely used, and their originals, which are usually not used at all. That is, everyone says 'P.S.,' 'a.m.,' and 'et al.' but no one says or writes 'post scriptum,' 'ante meridiem,' or 'et alii.' Similarly, 'etc.' is pronounced 'et cetera,' and 'vs.' is pronounced 'versus,' but both are normally not written out, just as 'Mr.' is normally not written 'Mister.'

As for 'in medias res,' isn't it common enough to those of us who remember our English classes? Starting a story in medias res is one of those literary techniques that every student of English lit has to memorize, and I agree with Sherlock that that's the usual context, even if the original grammar implied jumping in in medias res (note BTW that both 'in's are required). But even assuming that 'Let's got' was only a typo for 'Let's go,' I agree with Mike E. that it doesn't work at all outside that specific literary context.

I'm not convinced that BE uses more Latin than AE. I would say instead that in English in general, the trend is away from unnecessary bits of Latin in educated writing. Also, German and English usage of Latin just isn't always the same. Some Latin phrases used in German academic writing may not be used at all in English (I've seen this in the forum, especially among historians, theologians, philosophers, etc., though no examples come to mind at the moment). And the opposite is also true; many Latin medical terms, for example, are fairly everyday in English but uncommon in German except among doctors.

Also, many Latin phrases adopted into English have changed their meaning or grammar slightly, like 'non sequitur,' 'in medias res,' and 'sine qua non.' And pronunciation isn't always consistent either; see this parallel thread on Latin pronunciation in English:
  related discussion:pronounciation 'vice versa'?

So the safest bet is probably to double-check definitions and pronunciation in a monolingual dictionary, and compare usage in standard educated English, such as online newspapers or magazines. Or to browse here in the archive, if the links ever work again.

@hm

I think 'ceteris paribus' may be more common in British English, particularly in Economics literature. I would expect it to be used by people who also say "the man on the Clapham omnibus", which I presume is also rare in the U.S.

I thought I had heard 'in medias res' only in German but, now you mention English lessons, it does ring a bell.

I am a Law student in England, and much of hat has been said is true. However, I remember it being said in my first year of study, that latin was unnecessary in texts and being phased out. The odd phase is okay, but they don't like you to go mad with it. I believe it was the Wolf Reform that decided upon this, so to make legal documents easier to understand for people outside of the law.

Don't you find rather funny that we are all missing the wood because of the trees?
Or did anyone mention "FORUM"?

@hm--us: I am impressed by the categorization by Garner, which I find very, very reasonable (why didn't I think of it myself???)
About categories 3 to 6 being dangerous territory, yes, that's true. Nevertheless they are also a sort of perverse status symbol allowing people who were inflicted Latin in their green years to feel like veterans of the same war: whenever someone says "carpe diem" instead of "let's enjoy the day before it starts raining" you experience that warm feeling of 'being among peers' (it's deplorable elitarism, I know, that's why it's so fun :-)