I’ve gotten reports from a few users that indicate that sometimes the client’s locale ID is set inconsistently.
In one case the locale Id was incorrectly set to some non “en-us” id in rare cases, seemingly at random. In the case linked above, the user reports that the locale Id is consistently “en-us” when the client is launched from the windows store, and “nl-nl” when launched from a browser.
This is intended behavior: if you launch a game without a preferred language set in Roblox account settings, it will use the browser locale as default when launching from browser, and the device locale when launching from the Windows store app.
To get a consistent locale, the user should just set their preferred language in settings.