Could you be more specific please. Do you mean srcpac doesn't print messages in your locale? or do you mean pacman printing out localized messages is breaking srcpac?

example:
line 360:
echo -n "Proceed with upgrade? [Y/n] "

srcpac is waiting for Y/n in english, but pacman is waiting for O/N (oui/non) in french

This can be fixed in srcpac only by adding gettext support to it, I guess.

I want to notice that in Russian translation, for example, pacman waits for Y/n
e.g. Y/n was intentionally not translated to not force users to switch keyboard layouts just for answering to question (except default answer).

Short term hack would be to pass LC_ALL|LANG=C to pacman inside srcpac.

Better solution should come eventually. srcpac needs a decent rewrite of some parts to deal with the switch to both pacman and makepkg 3. I should get around to doing this soon and submit some changes upstream. This will hopefully resolve all srcpac bugs currently listed in Flyspray.

Wait, I don't see any bug here.
srcpac does the question and it waits for Y or N. Not pacman.

I checked to code and indeed srcpac does its own parsing of Y/n and not makepkg/pacman. Closing as "not a bug" given there is not response from submitter to clarify.