BuddyPress.org

You have to add a define line in your bp-custom.php.

Say you have your languages files called piglatin.mo and piglatin.po.

Upload the files to /wp-content/plugins/buddypress/bp-languages/.

Then this is what you’d put in your /wp-content/plugins/bp-custom.php:

define( 'BPLANG', 'piglatin' );

if ( file_exists( BP_PLUGIN_DIR . '/bp-languages/' . BPLANG . '.mo' ) ) {

load_textdomain( 'buddypress', BP_PLUGIN_DIR . '/bp-languages/' . BPLANG . '.mo' );

}