Switching the language doesn't affect `Intl.Numberformat`

[schuetzm]

Switch to German, open browser console, try this:

formatter = new Intl.NumberFormat(undefined, {
    style: 'currency',
    currency: 'EUR',
});
formatter.format(10)

Result: "10,00 €"

Then switch to a different language, reload the page, run the same code. The result is still "10,00 €"; it should have been "€10.00".

[M-Reimer]

Actually that's just one of a few "Intl" methods:
https://developer.mozilla.org/en-US/docs/Web/JavaScript/Reference/Global_Objects/Intl
I'm not sure if I want to open that can of worms.
To make this possible, every one of those would have to be hooked, redirected into the Add-on and then modified to work differently if the language is not defined.