Plural forms support

[diversys]

See discussion here:

0c2e4a2#commitcomment-13812540
In English there are only two forms: plural and plurals.
However, in Russian, Polish and some other languages there are three, depending on amount:
1 - пакет, from 2 to 4 it's "пакета", 0 and starting from 5 it's "пакетов"

See also here: https://dev.haiku-os.org/ticket/10755