Thanks for helping us get ClassicPress translations moving again.
“this is something we will do at a team lead level” - who specifically will be taking this on?
It makes sense to me to add en_GB and use that to draft a process for adding new locales, but not to set en_GB as the new default locale. There would be two ways to do this, both with significant drawbacks - changing all the strings in core (lots of work), or forcing all installations to download the en_GB translations and use them by default (hacky, extra files and network requests).
We had a call for volunteers 3 months ago (December 2019): Call for volunteers to translate ClassicPress Contacting the people who expressed interest there would be a good next step.
Definitely agree with this. We also have several languages that may not meet these criteria at the moment (e.g. Turkish, Japanese, two variants of Portuguese) and we need to decide what to do with these also.
This is worthy of a separate topic but I don’t think we know the answer yet.