大连是中国最美的海滨城市。翻译成英文

Dalian is the most beautiful seaside city in China.

第一,要用the,不能用a.
第二,如果要加上one of的话,就应该变成one of the most beautiful seaside cities,注意是city的复数形式.

Dalian is the most beautiful sea town of Chinese!
这才是正确的!我外国朋友说的,哈哈!

Da Lian is the most gorgeous coastal city in China.

Da Lian is a most beautiful coastal city in China

Da Lian is the one of the most beautiful coastal cities in China.

你的"最美"只是中文的理解，在外语中，应当用“之一”，即one of.

Dalian is the most beautiful seaside cities in China.