Working with ESL people makes it clear that grammar isn't so important. One of my friends would say, instead of "go shopping", would say "make some shoppings". Instead of "it's time to go", he'd say "time for go". All words that started with 's' were pronounced 'ehs', as in "gas ehstation".
The other people at work soon picked those lines up, and we used them regularly amongst ourselves. I still use them decades later!
English is a fault tolerant language that is usually comprehensible with errors. That isn't generally applicable to all languages.
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!
This is grammar from their native language. They dont know the English grammar, so they just assume it's the same as the one they understand. You just understand them via the context.
Older Europeans used to say 'AND NOW WE MAKE PARTY!"