sourceName can be specified but is ignored; actually using it (passing it to MessagesParser) would allow for better exception messages, i.e. "Configuration error in messages.de:909" instead of "Configuration error in :909"

2.3.x
https://github.com/playframework/playframework/blob/2.3.x/framework/src/play/src/main/scala/play/api/i18n/Messages.scala#L197

master
https://github.com/playframework/playframework/blob/master/framework/src/play/src/main/scala/play/api/i18n/Messages.scala#L239