My experience with a large multi-thousand Eng department where the majority are in the US or UK: US-based or influenced employees will write usually with American English spellings and continue to do so even if based in the UK. UK-based or influenced employees will write with British English spellings and continue to do so if based in the US. No one conforms to the other and everyone can understand each other perfectly fine because the spelling of these words does not matter for comprehension. This applies to writing as well as words in code or API names.