wp-includes/class-wp-locale-switcher.php:189Returns the locale currently switched to.
string|false public function get_switched_locale() { $entry = end( $this->stack ); if ( $entry ) { return $entry[0]; } return false; }Introduced in 6.2.0. Unchanged from 6.7.7 through 7.1.0.
Signature, return type and hooks compared across 5 parsed releases.
src/wp-includes/class-wp-locale-switcher.php, and regenerated for each WordPress release so it tracks the code rather than a snapshot of it.