"It's common all over the world, not just in Japan."
"It isn't common just in Japan but around the world too."
"Not just in Japan, it's common in other countries too."
"It's common all over the world, not just in Japan."
"it's common" 「共通」
"all over the world" 「世界中で」
"not just in Japan" 「日本だけではなく」
"It isn't common just in Japan but around the world too."
"It isn't common just in Japan" 「日本だけで共通ではなく」
"all around the world too" 「世界中も」
"Not just in Japan, it's common in other countries too."
"in other countries too" 「他の国にも」
"common" の代わりに "prevalent" も使えます。よく行っていると言う意味です。
"It's prevalent all around the world."
I think there are more people around the world who are hesitant to get married, not just Japanese.
この場合、次のような言い方ができますよ。
ーI think there are more people around the world who are hesitant to get married, not just Japanese.
「結婚するのに及び腰な人は、日本だけでなく世界中にたくさんいると思う」
hesitant で「ためらって・気後れして」
ご参考まで！
オーストラリア 
カナダ 
