I think his name is called “Van gGogh” except for Japan, but his name is called “Gohho” (ゴッホ) in Japan.

I’m not familiar with Van gGogh, but I’ve seen his paintings, like Sunflowers, Cafe Terrace at Night and his self-portraits etc.

However, ithey were replicas.

I’ve never seen the originals of his paintings.

I’ve read it that he was so short-tempered that he cut off his own ear.

About Van gGogh!

I think his name is caspelled/pronounced as “Van gGogh” except for Japan, but his name is caspelled/pronounced as “Gohho” (ゴッホ) in Japan.

Before, I didn’t even think that the pronunciation of his name accent was different.

I’m not familiar with Van gGogh, but I’ve seen his paintings, like Sunflowers, Cafe Terrace at Night, and his self-portraits, etc.

However, ithey were replicas.

or: "However, the ones I saw were replicas."

About Van gGogh!

I think his name is called “Van gGogh”, except forin Japan, but his name is called “Gohho” (ゴッホ) in Japan.

The first part of the sentence already says 'in Japan' so you don't need to say 'in Japan' at the end too.

Before, I didn’t even think that his name accent was different.

However, ithey were replicas.

I’ve read it that he was so short-tempered that he cut off his own ear.

About Van gGogh!

I think his name is called “Van gGogh” except for, but in Japan, but his name is called “Gohho” (ゴッホ) in Japan.

- you can just say "his name is", it sounds more natural
-Capitalize the first letter of each name
-"except for Japan" is not necessary because you are only talking about Japan. Since you are specifically talking about Japan, you can say "but in Japan"

Before, I didn’t even think that his name accent was different.

-"Accent" in English is related to how you pronounce or speak a word. In this case, Gohho is completely different from Van Gogh so you can just say his name is different.

However, ithey were replicas.

You can usually use "they" as plural for "it"