My thoughts on this is a function to get such and such data. Log whether the bot is D2 or D2 LoD, and whether it's an Azeroth or USEast (in the case of USEast server, otherwise Lordaeron/USWest and so on) client. LoD and D2 would come back as the Starcraft-style server realms, while only Warcraft III: RoC and Warcraft III: TFT would come back as the Warcraft-style realms. AKA: If the bot is not WC3 or W3XP, then it counts as the SC-style, and if it is, it'll be logged as WC-style. Then the plugin could check if the joining person is WC- or SC-style, and message accordingly. If the bot is SC-style and the joiner is SC-style, it uses a realm void. If they're opposite server styles, it uses the appropriate realm (by calling data from the bot's login plugin on which server it's on) and messages. Only with D2/LoD bots would it require to use the asterisk before a whisper message.
And, yeah, I have no idea how to write that in Java. >_> Darn my downfalls.