ANSWER:
Quran can be understood by the masses in general such as the prohibition of riba, zina, stealing, killing etc.
Also the instruction to pray and give zakat is quite obvious and clear.
The problem is when one doesn’t speak Arabic fluently and doesn’t know the sunnah of the prophet salla allahu alaihi wa sallam and claims that he can understand the Quran! Such a person is delusional.
He is relying on the interpreter’s understanding and without proper knowledge, he would be like a layman trying to perform a surgery on the spine of a sick person. If he doesn’t kill him, he will make him paralyzed for life.