英訳です。

日中国交正常化から40周年を迎えるというのに、両国の間にはとげとげしい空気が漂う。こんな時だからこそ、市民がコツコツと積み重ねてきた交流の大切さを思い知る。

Altough forty years passed since Japan and China signed the diplomatic treaty, they will possibly have a conflict. It is in this time that I know the importance of the friendship people established gradually.

としてみました。どうでしょうか

the resumption [normalization] of diplomatic ties between Japan and China (出典:eプログレッシブ英和中辞典/プログレッシブ和英中辞典)
日中国交正常化
のようですが、僕の英語力ではこれが限界(^^;;

No.1 ベストアンサー 回答者： sayshe 回答日時： 2012/09/04 09:26

＜試訳１＞

Although forty years have passed since diplomatic relations between Japan and China were normalized, territorial disputes between the two countries have become worse recently. At such a difficult time, I am more sharply aware of the importance of friendship that has been built up patiently by the citizens of both countries.

＜試訳2＞
It has been forty years since Japan and China became friends again after World War II, but recently there is a bad atmosphere between the two countries. Such a difficult time makes us realize more strongly how important it is for citizens of both countries to have kept up mutual exchange patiently.