Hola, could you help me - I would like to know how to say "we will understand (each other)". Creo que "entenderemos" es tontería.
Ah, then I would say "Espero que nos entendamos bien.
You don't really need the future tense here, but it must be the subjunctive mood because the subject is plural. "Hope" is esperar, not creer. You could also say "Ojalá que..."
Just to clarify:
Creo que nos entenderemos bien. (I hope we will understand - each other - when we will communicate in Spanish).
"Nos entenderemos (uno al otro)" is not a tontería. Give us the full context and we might suggest an improvement, but there's nothing wrong with it.