There is truth to that, but how do you reconcile:
1Cr 14:2 For he that speaketh in an [unknown] tongue speaketh not unto men, but unto God: for no man understandeth [him]; howbeit in the spirit he speaketh mysteries.
The clear plain teachings doesn't seem as simple as you imply.
Since the obvious nature of tongues being genuine languages, then the verse you just cited must be reasoned with that in mind.
There is no clear teaching in that verse hat the language spoken by that man is a foreign never to be understood language, only a language that no one was there to translate, and that would therefore only be understood by God.
Since Angels are spiritual beings, whatever they speak might be called a spiritual language, but we are not spiritual beings are we? We are fleshly beings, and we would therefore speak fleshly languages. "That which is of the Spirit is Spirit, and that which is of the Flesh is Flesh" (John 3)
My point in the quote you cited, though, was that tongues are NOT a sign for believers, and the modern Charismatic movement claims it is a SIGN FOR BELIEVERS to prove they have received the Spirit.
The Bible says it is a sign for UNVBELIEVERS.
To claim something is for Believers when the Bible says it is for UNBELIEVERS, that is totally unbiblical.
1Cr 14:2 For he that speaketh in an [unknown] tongue speaketh not unto men, but unto God: for no man understandeth [him]; howbeit in the spirit he speaketh mysteries.
Easily. I go over to Japan to a small village that only speaks Japanese, and I go to the worship and during testimony time I tell how God has saved me. ANd, the only response I get is, "No speaka Ingrish."