You're going to do that even when you're in Japan?
「それって日本にいる時でもするの?」は英語では You're going to do that even if you're in Japan? になります。
You're going to do that even if you're in Japan?/You're going to do that even when you're in Japan?
「それって日本にいる時でもするの?」の「〇〇にいる時」は英語で even when you're (〇〇)です。
例えば
Are you doing to do ramadan even when you are in Japan
ラマダンって日本にいる時でもするの?
Do you use chopsticks even when you are in the United States?
アメリカにいる時でもお箸を使いますか?
Do you refrain from drinking alcohol even when you go to a nightclub?
クラブに行く時でもお酒を飲めないの?
ご参考までに。