I just openend a costume trunk (Box of Turkish Delight) but I did not get the achievement.

Is this because it's not a good trunk or did I do something wrong?

You have to open this item:

Oh, it's not just any costume trunk. I should have read better. :)

Thanks for your help!

You are welcome.

That trunk is the prize for getting the 5000 clothes in wardrobe achievement. And it now gives you 500 CSC when you open it.

Aha, that's good to know. I'll just have to keep saving clothes and I'll get 2 achievements in 1 plus CSC to spend!