[moses-palmer]

What about gettext _N? I have used a library with a similar interface, and we didn't even get complaints for Slavic languages with very complex pluralisation rules.

[jwilk]

GNU gettext has pretty good support for translating messages with numerals:

https://www.gnu.org/software/gettext/manual/html_node/Plural...

https://www.gnu.org/software/gettext/manual/html_node/Transl...