Authors:

When you speak in other tongues, no one understands what you're saying, because you're speaking to God. It's a direct communication between your spirit and God. You're speaking the language that only He understands.

Chris Oyakhilome PhD (2013). “How to Pray Effectively: Volume One: Understanding the Rules of Prayer for Different Situations and How to Apply Them for Your Desired Outcome”, p.39, Lulu Press, Inc
When you speak in other tongues, no one understands what you're saying, because you're speaking to God. It's a direct communication between your spirit and God. You're speaking the language that only He understands.