But your friend was applying consistent rules of grammar from his mother tongue. Having learned some vocabulary, he would mentally form the phrases in his head, and then literally translate out the words and tenses.

Grammar was so important to him that he was adhering to the grammatical rules he knew. It would be interesting to know how he would perform with writing or typing instead of contemporaneous conversation.

"go" in particular is an irregular verb, and also one of the most versatile words in the English language. Having studied how to conjugate "go" in other languages, I do not envy anyone trying to conjugate or just use it in an English sentence!