wp-includes/l10n/class-wp-translation-controller.php:76Returns the current locale.
string public function get_locale(): string { return $this->current_locale; }Introduced in 6.5.0. Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-includes/l10n/class-wp-translation-controller.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.