wp_set_lang_dir() │ WP 3.0.0

Sets the location of the language directory.

To set directory manually, define the WP_LANG_DIR constant in wp-config.php.

If the language directory exists within WP_CONTENT_DIR, it is used. Otherwise the language directory is assumed to live in WPINC.

Internal function — this function is designed to be used by the kernel itself. It is not recommended to use this function in your code.

No Hooks.

Returns

null. Nothing (null).

Usage

wp_set_lang_dir();

Changelog

Since 3.0.0 Introduced.

wp_set_lang_dir() code WP 6.9.1

wp-includes/load.php 
function wp_set_lang_dir() {
	if ( ! defined( 'WP_LANG_DIR' ) ) {
		if ( file_exists( WP_CONTENT_DIR . '/languages' ) && @is_dir( WP_CONTENT_DIR . '/languages' )
			|| ! @is_dir( ABSPATH . WPINC . '/languages' )
		) {
			/**
			 * Server path of the language directory.
			 *
			 * No leading slash, no trailing slash, full path, not relative to ABSPATH
			 *
			 * @since 2.1.0
			 */
			define( 'WP_LANG_DIR', WP_CONTENT_DIR . '/languages' );

			if ( ! defined( 'LANGDIR' ) ) {
				// Old static relative path maintained for limited backward compatibility - won't work in some cases.
				define( 'LANGDIR', 'wp-content/languages' );
			}
		} else {
			/**
			 * Server path of the language directory.
			 *
			 * No leading slash, no trailing slash, full path, not relative to `ABSPATH`.
			 *
			 * @since 2.1.0
			 */
			define( 'WP_LANG_DIR', ABSPATH . WPINC . '/languages' );

			if ( ! defined( 'LANGDIR' ) ) {
				// Old relative path maintained for backward compatibility.
				define( 'LANGDIR', WPINC . '/languages' );
			}
		}
	}
}