Allow for UK + US English as multilingual

[Fmstrat]

Is your feature request related to a problem? Please describe.

When working with those in the US and the UK, it is common to need to have the unique spellings of words for UK and US English together without having to switch languages. Currently, you cannot select English US and English UK as multilingual to merge the dictionaries.

Describe the solution you'd like
The addition of both English options to the multilingual selection.

Describe alternatives you've considered (if any)
I've tried adding the US dictionary to the UK language, and the UI sends me to Codeberg to download the file, but there doesnt appear to be a way to load the dictionary in for use with that language.