No. Paul says he will pray with the understanding also.
14 "For if I pray in an
unknown tongue, my spirit prayeth, but my understanding is unfruitful.
15 What is it then? I will pray with the spirit, and
I will pray with the understanding also: I will sing with the spirit, and I will sing with the understanding also." (1 Corinthians 14:14-15).
So Paul is not encouraging us to pray in some kind of secret prayer language.
Praying in the Spirit does not refer to the words we are saying. Rather, it refers to how we are praying. Praying in the Spirit is praying according to the Spirit’s leading. It is praying for things the Spirit leads us to pray for.
Romans 8:26 tells us, “In the same way, the Spirit helps us in our weakness. We do not know what we ought to pray for, but the Spirit Himself intercedes for us with groans that words cannot express."
Source used:
What is praying in the Spirit?