Translators should know both the source and target language well enough to know the rules for the different plural forms. Using a name here is probably just to

Translators should know both the source and target language well enough to know the rules for the different plural forms. Using a name here is probably just to have a key for them (and frankly, better than gettext's approach). The correct name apparently would be singular, plural, genitive plural, if I'm reading Wikipedia right, but that's a bit cumbersome to type every time.