Rethink localization API

[syeopite]

There should also be ways to modify how the format*_func are called for each of their usages. That way it'd be possible to change the way dates and duration are formatted in accordance to what element is being rendered

The way plurals work are also a mess and should be refactored.

Using a simple dict with "magic" prefixes and suffixes to denote functionality is definitely too native of a solution...