The Arabic phrase "Allahu Akbar" is commonly translated as "God is great". Yet the actual meaning goes beyond that. "Akbar" is closest to the comparative in English language, e.g., meaning "greater", not "great".
The phrase is not necessarily wrongly, but somewhat unsatisfyingly, translated with attributing the superlative to Allah, as in "God is the greatest" - because that would imply there was some kind of rank to this greatness that compares to us, and our own. Yet "Allahu Akbar" tells you that "God is greater" - greater than any of our finite measures of greatness, greater than what our senses can perceive. This way, the phrase becomes its own response: Whatever you imagine when hearing it, or saying it, whatever your measure or scale, Allahu Akbar.