What would be a good translation of "touché" from English to Latin? Translating the French participle gives tactus, but I doubt that will convey the same idea. Is there an idiomatic Latin expression that could be used in a similar way? I cannot think of anything better than bene or ita vero.
"Touché", to me, indicates that one is gracefully conceding a point in argument. It can also sound a bit pretentious to use the French loanword instead of plain English "granted".
With that in mind, I would suggest synchōrō.
This is (a transliteration of) the first singular present indicative active of Greek συγχωρέω. It's a verb with many different meanings; depending on context it can mean "combine, meet with" or "get out of the way of, withdraw from". But in rhetoric or debate, it means to concede or grant a point to your opponent. The first singular present indicative was used often in Plato, usually by people trying to argue against Socrates. And using a loanword, especially one which contains a non-native sound ("y"), gives it that slightly pretentious touch.
Example: Plato's "Republic" 1.335e (translation based on Shorey 1969):
"So if [someone suggests punishing lawbreakers], then he is no truly wise man. For what he meant is not true. For it has been made clear to us that in no case is it just to harm anyone." "Touché."
The Latin expression used by Plautus and then picked up by Erasmus (Adagia II, iv, 93), rem acu tetigisti, immediately came to mind as potentially useful in answering your question.
rem acu is a way of rendering the idea "point made". Here, the person is not "touched", but the matter is "touched by the point of a needle", i.e. with accuracy. Tetigisti is implied, but left out of the phrase.
acu tactus is a more direct way of saying touché using the same phrase as a basis.
Rem Acu. You have hit the mark; you have hit the nail on the head. Rem acu tetigisti (Plautus). A phrase in archery, meaning, You have hit the white, or the bull’s-eye.
“‘Rem acu once again,’ said Sir Piercie.”—The Monastery, chap. > xvi.
See Lewis and Short entry for acus, -us f. needle. Contrast is made between literal and figurative meaning.
acu rem tangere, to touch the thing with a needle, English, to hit the nail on the head
from Plautus, Rudens, 1306
Grip. Tum tu mendicus es?
Labr. Tetigisti acu.
See also L & S entry for tango, tetigi, tactum - there are multiple literal and figurative uses meaning to touch, to strike and to affect, among others.