WordPress at a glance
filter is not described

determine_locale filter-hook . WP 5.0.0

Filters the locale for the current request.

Usage

add_filter( 'determine_locale', 'filter_function_name_7203' );
function filter_function_name_7203( $locale ){
	// filter...

	return $locale;
}
$locale(string)
The locale.

Where the hook is called

determine_locale()
determine_locale
wp-includes/l10n.php 152
return apply_filters( 'determine_locale', $determined_locale );

Where the hook is used (in WP core)

Does not used.