In src/volume_key.c there is this helpful comment to us translators:
{{{
/ TRASLATORS: The "(y/n)" part should indicate to the user that input
matching (locale yesexpr) and (locale noexpr) is expected. /
}}}
I'm guessing the intention was that this should have been brought over to the pot file too. It isn't, however, since there is a misspelling in "TRANSLATORS". (I'm assuming TRANSLATORS is used as an --add-comments tag when extracting.)