When a Japanese anime is dubbed in English, it's only half as interesting.
When you watch a Japanese anime that has been dubbed in English, it loses half its appeal.
この場合、次のような言い方ができますよ。
ーWhen a Japanese anime is dubbed in English, it's only half as interesting.
「日本のアニメが英語に吹き返されてると、面白さが半減する」
it's only half as interesting. を使って「面白さが半減する」を表現できます。
ーWhen you watch a Japanese anime that has been dubbed in English, it loses half its appeal.
「日本のアニメを英語の吹き替えで見ると、面白さが半減する」
it loses half its appeal. を使っても「面白さが半減する」を表現できます。
ご参考まで！
カナダ 
