[Feature] Robustness

[ultravires]

What problem does this feature solve?

Update src/core/locale.ts:

const langStr = (
        /* eslint-disable-next-line */
        document.documentElement.lang || navigator.language || (navigator as any).browserLanguage
    ).toUpperCase();

const langStr = (
        /* eslint-disable-next-line */
        document.documentElement.lang || navigator.language || (navigator as any).browserLanguage || DEFAULT_LOCALE
    ).toUpperCase();

What does the proposed API look like?

Nothing.