Translation:I have to understand this question.
This seems like an odd sentence. Does it mean something like "I should know this" or like "I have to figure out what this question is asking"?
The latter, I would say.
i must understand this question. why not?
It's an okay translation. Feel free to report it.
How silly - "must" and "have to" are interchangeable in the English language. You are splitting hairs here!