last night I watched a movie that is named Dangal.
Last night I watched a movie called "Dengal"
["That is named" = "called". Dengal in inverted commas because that was the name of the movie.]
Dangal has become the best seller movie in bollywood history, and it has reached to the best 250 movies in IMDB list.
Dengal has become the highest grossing move in bollywood history and has reached the top 250 movies as rated by IMBD
[I corrected Dangal to Dengal. When talking about movies, you usually say "grossing" which is a way of saying it made the most money. "Top 250 movies as rated by IMDB" - I say this because this the list is made by IMDB and there are other lists which may be different, and don't rate Dengal as highly.]
This is a huge success.
In my opinion the most important reason of this success is that the first character is a woman, and it is about a fight between a woman and unwritten society rules.
In my opinion, the most important reason for this success is that the leading character is a woman, and it is about her struggle against societal rules.
[Firstly - great opinion! I also like that you said it was your opinion. "reason of this success" became "reason for this success" because we usually use "reason for" and "reason(s) why". "The reason for your success..." or "the reason why I say this is because...". I changed "first character" to "leading character" because this is most natural. If you fight something, its usually physical, like punching. When you struggle against something its usually a mental struggle.
because in the world history women's power haven't been seen and in most countries no one believes in women.
Because the power of a woman is rarely seen (In India), and people in most countries don’t believe in woman’s rights?
[I don’t think you need to state “world history” because its implied. I added “rarely seen (in India)” because you don’t often see woman standing up for their rights in India (not the world).