When Israel was exiled in the time of the wicked Nebuchadnezzar, they became interspersed in Persia and Greece and other nations. Children were born to them in these foreign countries and those children's language was confused.
The speech of each and every one was a concoction of many tongues. No one was able to express himself coherently in any one language, but rather in a mixture [of languages], as [Nehemiah 13:24] states: "And their children spoke half in Ashdodit and did not know how to speak the Jewish language. Rather, [they would speak] according to the language of various other peoples."
Consequently, when someone would pray, he would be limited in his ability to request his needs or to praise the Holy One, blessed be He, in Hebrew, unless other languages were mixed in with it. When Ezra and his court saw this, they established eighteen blessings in sequence.
The first three [blessings] are praises of God and the last three are thanksgiving. The intermediate [blessings] contain requests for all those things that serve as general categories for the desires of each and every person and the needs of the whole community.
Thus, the prayers could be set in the mouths of everyone. They could learn them quickly and the prayers of those unable to express themselves would be as complete as the prayers of the most eloquent. It was because of this matter that they established all the blessings and prayers so that they would be ordered in the mouths of all Israel, so that each blessing would be set in the mouth of each person unable to express himself.