It is said that Stephen King once said he almost never rereads books because "life's too short" for that.
I kind of agreed with him, but after all, I came to believe that reading the same novel twice might be sometimes worthwhile.
Eleven years ago, I picked up Stephen King's novel titled "Duma Key."
However, I couldn't finish it primarily because of my lack of English ability, so I read the Japanese translation instead at that time.
Today, after all these years, I finished reading the English original version on my Kindle.
I knew I didn't remember much even before I started reading, but I didn't know that the "didn't remember" part was this much.
In fact, I was so surprised by my loss of memory that I wondered if I might be developing Alzheimer's or something like that.
Or I might have been wrong about my belief that I must have read the novel once in Japanese translation. sembra naturale?

Excellent. Your tone and style is very natural – well done. There are a couple of small errors

I heard that Stephen.... -- try not to say "it is said", unless it really is a commonly understood saying. Also, try not to repeat key words in a sentence – two said's close together sound weird.

I kind of agreed with him, but after a while, I came to believe... -- "after all" is an expression unto itself, which does not fit your meaning

I read the Japanese translation instead. -- there is no need to say that you did it at that time. The time context is perfectly clear already.

I didn't know that I wouldn't remember THIS much -- in your context here, it's okay to simplify the statement with an emphasis in capitals. DO NOT OVERUSE THIS OR IT WILL SEEM AS IF YOURE SHOUTING.

Or I might have been wrong about my belief that I must have read the novel once before -- there is no need to repeat the fact that you read it in translation.