British English Localisation

[NoahC500]

Is your feature request related to a problem? Please describe.
Yes, I, and I imagine fellow Britons, am irritated when apps and programmes are only available in American (or some other form of) English.

Describe the solution you'd like
British/UK English (en_GB) be added to the Hosted Weblate. I would be very happy to contribute a chunk of time to it.

Additional context
When I tried to add it as a language, Hosted Weblate gave the error:

Select a valid choice. en_GB is not one of the available choices
This list includes only basic languages. Please contact project maintainers to add others.

Thanks