Will we Speak Japanese or English in Heaven?

Language barriers, differences and translations are sometimes a problem for people, but they are never a problem for God.

John Frame:
We don't know the language by which the Father, Son and Spirit communicate with one another eternally, but it certainly is not a language that we have ever heard on the street.
Indeed, that language is not a language that any human being has ever heard, even in God's conversations with us. Ear has not heard it (1 Cor. 2:9). What God says to the hearers of his divine voice is always a translation of his eternal thought, a translation from his divine speech to human speech. God tells Israel in Hebrew, or in some linguistic ancestor of Hebrew, that he is their Lord (Ex. 20:1-2).
Scripture never suggests that such translation distorts the divine words. His spoken words, so translated, as we have seen, bear his ultimate authority. They are God's personal words to human beings. They are infallible and inerrant... Language diversity has been a great barrier to human unity, but it has not been a barrier to God.