Improvement: Default language should be overridable

[RaphGL]

As of right now, there's no way of overriding language defaults. The website simply retrieves the preferred language from window.navigator and assigns it as the website's language. This should be changeable and in the settings section.

This will allow people to have languages that are not their system's default and will allow people to detect holes in the i18n for other languages they're maintaining that might not be their default too (I use EN_US but I contributed for the PT_PT translation and cannot switch between the 2 adhoc for example).