Turians speaking latin and Asari understanding them.

Garrus was fond of human sayings... I always assumed he understood the idioms he used, but of course he spent a lot of time around humans, what with working on the Citadel, then living on Omega, and being part of Shepard's crew.

On the Ship's little message board thing, Jaal is teaching the crew Angaran words.

I guess it's weird she's using it with Peebee, but Ryder is also listening, so eh. Probably best not to think too deeply about it, the problem of alien languages is glossed over as it is.

I'd be more shocked if a translator couldn't interpret Latin than not. Or that a species like the Asari didn't make it a point to learn Latin since most of our biology and medical sciences are labeled in the Latin language.

You know, Chinese and English is two very different languages, but they have different phrases for the same meaning. And when you translate one into another, you translate one phrase into another, even their literally meaning is different.

This is the 6437363rd example of BioWare being inconsistent on linguistics and how the translator works. This particular issue being dealt with seriousness and consistency is a ship that has long sailed, it's become a feature by now.

*knocks over Ryncol*

The translator. It just works, damnit! Hehe

What's good about a point founded on a basic miscomprehension of how communication works in the MEU?

Total consistency wouldn't really be necessary. At any level of proficiency below total fluency, some idioms would be understood correctly and others not. It's very easy to imagine a ltranslator (or a speaker, doesn't matter) understanding "quid pro quo" while not understanding the far less common "fly in the ointment."

Quid pro quo would be pretty much mandatory for a translator, since it's used so often in political and legal contexts.

Just to throw it out there, but Brits still use the term "quid" as slang for various amount of our currency (i.e. 20 quid is 20 pounds).

(And it just occurred to me that i.e. itself qualifies as another gratuitous bit of latin that we still use, since it's an abbreviation for id est  "it is". The same is true of e.g. being exempli gratia  "for the sake of an example".)

As others have said, the translator probably replaces various idioms and phrases with similar expressions spoken by other species, so they understand the concept the speaker is trying to convey.

The phrases "Quid pro quo", "tit for tat" or "you rub my back" would sound like complete gibberish to an alien race, as even if they tried to translate it directly, they wouldn't understand that it means someone asking for something in exchange or a favour.

It would be far easier for the translators to find and replace expressions that share similar meanings, rather than confusing the listener with cultural idioms of another species, that they don't fully understand or don't really translate well.

That said, we have seen various aliens comment on or muddle up certain human expressions.

Shepard had to correct a Turian in ME1 who said "A fly in the lotion" rather than "ointment", as well as the Asari socialites in ME3 who said "a stiff one in the lips", rather than "stiff-upper-lip".

The Anagara definitely have trouble following Ryder at times, due to their unfamiliarity with certain human expressions. Such as their non-plussed reaction to Ryder's awful dad jokes on Voeld about the "warm welcome" they received and trying to use humour to "break the ice".

*Lifts Ryncol*

It doesn't matter which one I might be referring to.  What matters is the possibility that an advanced VI would be able to take words that represent ideas from one species and translate them into words representing those same ideas for another species.  

It's kind of like "The Milky Way" and "Andromeda".  I'm mostly sure that Turian's, Quarian's, and Angara did not all decide independently to call these galaxies the same thing.  However, where in English we call our home galaxy "The Milky Way", Quarian's might call it "Spirally McSpiralface".  But the literal translation of what they are saying is then not important, according to the programming in the VI.  It's the meaning.  And so when they refer to the galaxy using the Quarian name, English-speaking humans will hear, through the translator, "The Milky Way."  

And so it is with "Quid Pro Quo."  Vetra says something in the Turian language that is most equivalent to the English-adopted Latin phrase "Quid pro quo" and so that is what he hear.