Muslims think Arabic is some kind of special holy language of God, like Jews think Hebrew is some kind of special holy language of God, even though Arabic sounds like you're talking with your mouth full and Hebrew sounds like you're hacking up a hairball. It's all supremacist nonsense. God's language is spiritual, and if there is some special tongue spoken in Heaven, it's none we know. This hand thing is just an example of pareidolia, or seeing the shape of things you recognize where they aren't really there, like looking at the clouds and seeing a fluffy bunny rabbit.