twitchnotify sends these as normal PRIVMSG messages. The message never contains tags at the moment and the first word will be the display name of the subscriber. This can be localized for asian users.
:twitchnotify!twitchnotify@twitchnotify.tmi.twitch.tv PRIVMSG #nl_kripp :Desmora just subscribed with Twitch Prime!
:twitchnotify!twitchnotify@twitchnotify.tmi.twitch.tv PRIVMSG #twitchpresents :Necktop just subscribed!