For follow-up discussion and general commentary on the topic. Comments are sorted chronologically.
I am inclined to agree with Mr. Houdmann. No case exists in the Bible where an angel spoke in what appeared to be an unintelligible language. They always spoke in the language of the people who were receiving the message.
Unintelligible foreign languages were often barriers to communication (like the Tower of Babel), not bridges to communication, curses not blessings.
One other aside. The OT promise to Israel to give foreign tongues were to prove God's message need not be in Hebrew. They apparently felt their race and language to be more special than any other.