I figured out a fix!
Logging out of my Microsoft account on the Glance page, clearing Windows Launcher cache, restarting, then logging in again seems to have sorted it out. It looks like Windows Launcher does not actually sync the settings (like locale) after the initial onboarding, and this triggers it. Another bug i found along the way is that it also does not update the account's avatar on the Glance page - even after logging in and out.