I18n cleanup

[SamMousa]

The idea of this PR is to clean up the i18n code a bit:

1. Instead of importing the full mutable object everywhere we just import a reader getString()
2. For new translations we export a registration function instead of writing to the object in multiple places.

The goal of this is to create some abstraction instead of having a global, largely untyped, object being changed everywhere in the code.
I'd like feedback on point 2 before I apply it to all translations.