The union jack for en-GB, but I'd say the UK flag useful regardless. Even for selecting en-US! No one outside native english speaking countries really cares de

The union jack for en-GB, but I'd say the UK flag useful regardless. Even for selecting en-US! No one outside native english speaking countries really cares deeply about what way color is spelled in a web shop, and everyone recognizes the flag(s). Having a flag doesn't preclude showing "en" or "English" next to it either. But I wouldn't confuse users with full ISO codes like en-GB or en-US. Just "en" and it can be the natural en of the site location. Everyone expects en to be en-US for a US site.