So I was wondering which achievements give you the titles "Fashionable" and "Celebrity" ?

The Fashionable title is from one of the Filled Wardrobe tiers.

According to the Subeta wiki, the Celebrity title is from one of the retired achievements when we had to find the missing book pages for Alexander a few years ago or whenever that was.

Aww man, of course they had to be very hard to get or totally unavailable xD

But thank you anyway!