What's the 'localize' and '$$$' 's meaning?

if ( documents.length > 0 && DocumentMode.RGB != activeDocument.mode ) {  var message = localize( '$$$/JavaScripts/WarnIfRGBSaveMessage=Your document is not RGB. Do you want me to switch and resave?' );  if ( confirm( message ) ) {  SwitchAndSave();  }
}