"I want such an umbrella."
Translation:Jag vill ha ett sådant paraply.
Yeah, imagine walking with your son in the store, you promised to buy him an umbrella of his choice, and he looks around and points at one and says: I want that one! In Swedish he might say: Jag vill ha ett så’nt! If you include the noun it would be Jag vill ha ett sådant paraply.
I actually don't find the English sentence that odd.
Imagine you're going for a walk and you see somebody with the coolest umbrella ever. You poke your partner and say: "Wow, look at that umbrella! It is sooo cool. I want such an umbrella." You won't stop the person and buy their umbrella, you just want to find a similar one, probably even in a different color, but with the feature that got you interested in the first place.