SVGHMI: Add "lang" permament persistent HMI_LOCAL variable to reflect selected language, apply stored language choice at startup and make it always subscribed to a pseudo widget (as for hearbeat) that apply language choice when it changes.
<?xml version='1.0' encoding='utf-8'?>
<SVGHMI xmlns:xsd="http://www.w3.org/2001/XMLSchema" OnWatchdog="echo Watchdog for {name} !" OnStart="xdg-open http://127.0.0.1:{port}/{name}" OnStop="echo Closing {name}" WatchdogInitial="10" WatchdogInterval="5"/>