DOMParser errors leak locale
While writing a test for #30304 (moved) I found (yet) another way to get browser locale:
const doc = (new DOMParser).parseFromString('getyourlocale', 'application/xhtml+xml');
alert(doc.getElementsByTagName('parsererror')[0].firstChild.textContent);
test: https://acatarineu.github.io/fp/locale_domparser_error.html