I would love to visit a lot of countries, but Iif I'm required to choose one, I would choose Japan. I would love to visit a lot of countries, but if I'm required to choose one, I would choose Japan.

I would love to visit a lot of countries, but Iif I'm required to choose one, I would choose Japan. I would love to visit a lot of countries, but if I'm required to choose one, I would choose Japan.

I would love to visit a lot of countries, but Iif I'm required to choose one, I would choose Japan. I would love to visit a lot of countries, but if I'm required to choose one, I would choose Japan.

I would love to visit a lot of countries, but Iif I'm require had to choose one, I would choose Japan. I would love to visit a lot of countries, but if I had to choose one, I would choose Japan.

Alternatively: "...but if I were required to choose one..."

I got very curious about their culture and society. I got very curious about their culture and society.

This is absolutely correct and likely what you would say when speaking. In formal writing you would want to say "I became very curious about their culture and society."

When I was a teenager, I used to watch a lot of Japanese animes. When I was a teenager, I used to watch a lot of Japanese animes.

When I was a teenager I used to watch a lot of Japanese animes. When I was a teenager I used to watch a lot of Japanese anime.

"anime" is one of those words that is its own plural.

When I was a teenager I used to watch a lot of Japanese animes. When I was a teenager I used to watch a lot of Japanese anime.

You could go either way, honestly, but "anime" sounds more natural to me than "animes".

I think it iswould be a good country to visit. I think it would be a good country to visit.

Your sentence worked grammatically; however, the conditional would be more natural here in my opinion.