On the Affinity website, I can get the spelling of color/colour to change depending on whether I go to the /en-us or the /en-gb version of the site (stick that in the URL - you'll see). Interestingly - there is no localization for us Canadians - we just get served the US version of the site, though it DOES know that we're in Canada and shows us the pricing in Canadian dollars. Weird, since our spelling is mostly, but not entirely UK spelling - not US (exceptions: aluminium...which really is a strange one since EVERYWHERE else uses aluminium, not the North American "aluminum", "localize" and other "ize" words are preferred here, over "localise" which is more common in the UK and Australia, "buses" - not the UK "busses", "license" for the noun and "license" for the verb etc. It can be challenging when spellcheck keeps changing or insisting on the other version, LOL.
I have Publisher and Photo and both use Canadian spellings in the menus (colour, not color) - I assume because I have Canadian English chosen for my Mac in the language preferences, but in Affinity Publisher, because I do work for some US clients, I simply have "English" chosen in the spell check. BTW - if you look closely at the screen grabs on their website, they also have "colour" - when en-us pages are loaded and the text on the site is the US spelling. (swapping out the language is relatively easy - swapping out images to match local language would be a major pain).
While none of these apps are internet-related, some languages, such as HTML/CSS/PHP - are all written in English, with American spellings (having been developed in the US), and I think in the name of standardization, this has resulted in many software developers worldwide adopting American spellings as standard. It could get pretty messy otherwise. The main thing is to be consistent - Affinity apps are written in C++ and Objective C - neither of which has a lot of set terms, apparently.
BTW - Adobe Creative Cloud just serves up American English. They don't even have the option of British or Canadian English - it's just "North American English" - rather arrogant of them, eh? The other option is "International English" - whatever that is. However, within the apps like InDesign, in the spelling preferences you can select UK or Canadian English - but the default is US in the user interface as far as I can see.
