Formal:
* Très fabuleux/fabuleuse: This is the most literal translation and conveys a sense of grandeur and wonder.
* Extrêmement fabuleux/fabuleuse: This emphasizes the intensity of the fabulousness.
Informal:
* Super fabuleux/fabuleuse: This is more colloquial and emphasizes enthusiasm.
* Trop fabuleux/fabuleuse: This conveys that something is "too fabulous" in a positive way.
* Fantastique! Génial! These words are less literal but express strong approval and excitement.
Slang:
* Canon!: This slang term means "gorgeous" or "amazing" and is often used for people or things that are very attractive or impressive.
* Dingue!: This means "crazy" or "wild" and can be used to express excitement about something that is very unique or memorable.
The best choice will depend on the specific situation and your desired level of formality.