We host a copy of the en_GB one as well. So if you can split out the UK spellings ones into a separate list I can try to update both as appropriate.
See this list of local dictionaries we install for Windows and macOS users.
https://github.com/Sigil-Ebook/Sigil...s/dictionaries
Of course users can supply their own hunspell dictionaries to replace these if they want.
Thanks!