You put the variable in as a string - that's why it's doing that.
Code:
SendChatMessage("my message will go here when ive spelled checked it", "WHISPER", "COMMON", unitpopupFrame.name)
edit: also, if you put nil instead of language, then it will use the default language for your faction (which would make your addon work for both horde and alliance).
Code:
SendChatMessage("my message will go here when ive spelled checked it", "WHISPER", nil, unitpopupFrame.name)