Different behavior between gettext and PHP implementation for unknown plural translations

[ArthurHoaro]

Note: this is a very minor issue you might not want to fix, but I wanted to report it since I came across it during my wrapper unit tests.

Issue: if the translation is unknown PHP's built-in gettext function will use English plural rules (fallback language) while Translator (translations loaded from PO file) will use the destination language plural rules.

Example:

English > French
French doesn't pluralize zero, while English does.

sandwich is an unknown key but a French translation is loaded

// with GettextTranslator
n__('sandwich', 'sandwiches', 0); // => sandwiches
// with Translator
n__('sandwich', 'sandwiches', 0); // => sandwich

[oscarotero]

It's interesting. I think we should unify the behaviours between two implementations, so GettextTranslator should be changed to mimic the native gettext.
I don't have enought time these days to face this. Do you want to work in a pull request?