ESR128 will leak/use your real en-* system locale when using en-US

something's not right and I have found non-deterministic results (AFAICT) - even when the locale is en-US - will fill in more details later

edit: or even worse, it's use_us_english_locale is not hooked up to all the Intl APIs and thus causes entropy right now. I think we shouldn't even be using use_us_english_locale because all resolved options are en-US (which is the locale we set) and therefore all Intl is already covered. The pref is causing discrepancies (depends on some OS factors IIUIC)

It's either broken now, or will be broken next ESR

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use_us_english_locale is deprecated come ESR128, and we need to check spoof english and setting the locale is enough