Add support for external translation tools

[vkbo]

Summary:

This PR adds support for importing translation files from a zip file that can be downloaded from an external translation tool, like Crowdin. All language files now also uses the fill "languge_country" style code.

Related Issue(s):

See discussion in #93

Reviewer's Checklist:

• The header of all files contain a reference to the repository license
• The overall test coverage is increased or remains the same as before
• All tests are passing
• All flake8 checks are passing and the style guide is followed
• Documentation (as docstrings) is complete and understandable
• Only files that have been actively changed are committed