汉译英：不鸣则已一鸣惊人，不飞则已一飞冲天！

Once sing，sing high。Once fly，fly up to the sky。
很简单的翻译,once表示一旦，先英文到汉语直白翻译就是一旦鸣叫，叫声很高，一旦飞翔，飞向天空。然后就会晓得是汉语的不鸣则已，一鸣惊人。不飞则已，一飞冲天

(of an obscure person)amaze the world by one\'s successful maiden effort.精选汉英词典 商务印书馆

此鸟不飞则已，一飞冲天；不鸣则已，一鸣惊人。（of an obscure personPto amze the world with the first work e.e. make(or pwll off) a great coup 汉英双解成语词典 商务印书馆

Does not fly then already, as soon as flies flushes the day; Does not call then, has surprised people.

Ming does not have blockbuster, has been flying off

Does not call has amazed the world with a single brilliant feat, does not fly has soared