It seems to me you have two UK language enabled in Cataloglanguage table. Make sure to check there.
I checked in the CatalogLanguage table, and it just has one entry for UK.
See the attachment :
Does that happen with newly created node? Or just existing node?
I'm guessing (obviously) but you might have versions in old language (en-GB perhaps), then you change it to en-gb
Where have you gotten those languages from?
I am not sure commerce will support anything but the two letter ISO language and region codes.
What I would have expected to see is languages such as 'en-GB' (english in great britain/united kingdom) and 'en-US' (english in united states of america).
Any tip how I can sort this now?
When it comes to data, I'd suggest to contact our developer support service and provide the information needed for investigation. I can technically tell you to try something, but it's not something I should do.
Including a region as UK that isn't a language at all? :P
I am having a very odd problem, for some reason in my catalog node when I open any content into edit I see Language (UK) appearing twice, although clicking any of the one makes both active.
Please see the attached image.
Any idea why its appearing?