I do not believe this is what the rules envisage. In the circumstances you refer no hail is necessary, the rule applies in any event. A form of hail may be considered evidential in a hearing. Hails are required in rule 20, I think that only is where the language exemption applies.

Catalan, I think I understand your question.

There are only 3 required “hails” in fleet racing covered by Introduction:Hails.  2 of these are presented in the rules in single-quotation marks (huh .. wonder why single-quotes are used instead of double-quotes?).

We had another thread which discussed the custom of calling for “water” as meaning “room to tack”  (can’t put my finger on it but maybe someone else can post it).  Personally, I would not have understood that as a hail for “room to tack” before that thread, however I probably would have understood it to mean a non-required request for room at an obstruction. 

If it is customary to call “agua” to mean “you owe me room” or “keep clear” then that is fine, but it is not “a hail required by the rules”, so it is not governed by “hails” in the RRS introduction.  Extra calls between boats like “agua” in your scenario can be considered a step one boat takes to avoid contact with another boat if the incident was before a PC.  There is a Case or US Appeal which states that, but can’t put my finger on that one either. 

PS: If someone knows the Case/Appeal that states a hail between boats is recognized as something a boat might do to avoid contact, please post it. 

Found 2 Cases: 41 & 107 that discuss hails not required by the RRS (emphasis added).

Case 41
"A discussion of how rule 19.2(b) and the definitions Obstruction and Clear Astern and Clear Ahead; Overlap apply when two overlapped boats on the same tack overtake and pass to leeward of a boat ahead on the same tack. There is no obligation to hail for room at an obstruction, but it is prudent to do so."

Case 107
"During the starting sequence, a boat that is not keeping a lookout may thereby fail to do everything reasonably possible to avoid contact. Hailing is one way that a boat may “act to avoid contact”. When a boat's breach of a rule of Part 2 causes serious damage and she then retires, she has taken the applicable penalty and is not to be disqualified for that breach.

THANKS YOU SO MUCH !!!