so is my word that goes out from my mouth: It will not return to me empty, but will accomplish what I desire and achieve the purpose for which I sent it. - Isaiah 55:11
"Word" here would not exclude the languages available in tongues. Tongues are words spoken from our spirit, which is exactly the type of word being spoken in Isaiah 55:11 because God is a Spirit, and Isaiah 55:11 only applies to God's word.
So as believers when we speak God's word from our spirit, it goes forth to accomplish that to which it is sent. Understanding of that word, is only required in our spirit... but God gave us the Spirit of Christ which understands all the words spoken, and tongues is always spoken from our spirit with full understanding in our spirit. It's ability to be effectual is not based on our mind.
As an example that was not even tongues, but groaning, I once woke up in the middle of the night groaning from my spirit. I saw my roommate downstairs sleeping, and my spirit ordered a demon to leave him while I was groaning. His life was changed afterward... so just imagine how powerful tongues is for God!!
-------------- More scripture came to mind:
For anyone who speaks in a tongue does not speak to people
but to God. Indeed, no one understands them; they utter mysteries by the Spirit. - 1 Corinthians 14:2
When we speak to God, we can ask God for things. We can ask God for things, for other people.
Yet you do not have because you do not ask. - James 4:2
If we turn that around, it matches Christ's statement: "Ask and you shall receive." But James is warning against carnal human desires for self-seeking... but if you ask in the spirit, there is no self-seeking for what you ask, and you shall receive!!!
And just as a side note, even let's say if you asked for something for yourself... "Let peace rest in my company, Lord!" Then God answers it, and nearby people are blessed.
The blessings of God overflow and bless others!
This is another way it would help others.