Improve translation of plurals

[clochix]

For now, we only handle one plural form for events duration and recurrence. But a lot of languages have several plural forms, so it would be better to use smart count every time we need to display a plural. See http://airbnb.io/polyglot.js/#pluralization

[jsilvestre]

Is it something we have a problem with currently? I mean with one of the language we support.

[clochix]

I remember one user on the forum mentioning that the plural for french was sometime wrong, so I created this issue as a reminder, but this is not a top priority, as I don't think we support for now language with several forms of plural.

[jsilvestre]

Fair enough, thanks!