Speaking 15 languages isn't even evidence of posession anymore. I know someone who met someone who knows 6 languages (English, Spanish, French, German, Samoan, and Italian?).
By the way, why would an Angel posess someone? God wouldn't "force" you into doing something for him, but if you refer to him as Lord, you would obey what he wanted. When you're posessed by a demon, you have no choice. For example, a pastor friend of my pastor met a lady once who was posessed by a demon, went over to a space heater, and started burning her arm right off, after demonstrating lack of skills at the worm, yet giving it an attempt anyhow. Who would volunarily do that?