It's a widespread Islamic phrase but yes it stems from Arabic it means "God is greatest" and is often chanted in celebrations in Iran (and anywhere else with high Islamic influence)

Many Muslims will use Arabic for certain religious/symbolic purposes regardless of native language as the Quran was revealed in Arabic so it holds special purpose and unites the global Islamic community as they all can understand such phrases no matter where they live/which language they speak.

As I posted the above comment there were reports of Iranians shouting it to each other from the rooftops and thousands taking to the streets in groups to chant it despite the threat of Israeli attacks to celebrate Irans successful retaliation.