Buddha or The Buddha usually refers to the person named Guatama, but the word is a title not a name, there are many Buddhas.
I think I read in a book by Thich that his language was lost but people he taught translated it to Pali and Sanskrit so we can compare those two translations to approximate what he taught.
Buddhism spread and often by the time it reaches English many things are lost in translation. Buddha taught 84,000 paths, and there are more than 80,000 books on the subject.
Buddha’s teachings are thousands of years old and are still being translated to English https://84000.co/.