Do we want more generic forms of naming like bootstrap names them and use sprintf to combine strings.

COM_KUNENA_ALERT_WARNING_X="Warning: %s"
COM_KUNENA_ALERT_ERROR_X
COM_KUNENA_ALERT_SUCCESS_X
COM_KUNENA_ALERT_INFO_X

Seems a bit cleaner and is reusable. I would not make this template specific though and make this part of the global language files.