"Extremely excellent" can be translated as "非常非常优秀" in Chinese.
This phrase is derived from the adjectives "非常 (extremely)" and "优秀 (excellent)" being repeated for emphasis.
Example Sentences and Translations:
"That performance was extremely excellent."
"那个表演非常非常优秀。"
"She did an extremely excellent job on the project."
"她在项目上做得非常非常优秀。"
"His work has been extremely excellent lately."
"他最近的工作非常非常优秀。"