Bugzilla

(In reply to Tom Ritter [:tjr] from comment #0)
> It was pointed out that `intl.regional_prefs.use_os_locales` can be set to True to ask the OS to format things (dates, not sure what else.)  
> 
> When RFP is enabled, we shouldn't be asking the OS to do anything, and we should be behaving deterministically.  I'm not sure if locking this pref to false is sufficient

I can answer this.
In Tor Browser 14.0a1 our patch to absolutely not leak regional locales from the OS broke.
The result was that my English GB VM reported `en-GB` in the resolved `Intl` options with an `en-US` browser.
In general, the `Intl` API automatically matches the OS region when the language part is the same. I tested also with browser the browser set in `it` (which is `it-IT`) in an `it-CH` OS. `Intl` reported `it-CH`. Same for various `es-...`.
Bug 1746668 is about a very similar topic.

(In reply to Tom Ritter [:tjr] from comment #0)
> It was pointed out that `intl.regional_prefs.use_os_locales` can be set to True to ask the OS to format things (dates, not sure what else.)  
> 
> When RFP is enabled, we shouldn't be asking the OS to do anything, and we should be behaving deterministically.  I'm not sure if locking this pref to false is sufficient

I can answer this.
In Tor Browser 14.0a1 our patch to absolutely not leak regional locales from the OS broke.
The result was that my English GB VM reported `en-GB` in the resolved `Intl` options with an `en-US` browser even when `intl.regional_prefs.use_os_locales` was set to `false`.
In general, the `Intl` API automatically matches the OS region when the language part is the same. I tested also with browser the browser set in `it` (which is `it-IT`) in an `it-CH` OS. `Intl` reported `it-CH`. Same for various `es-...`.
Bug 1746668 is about a very similar topic.