"I add new friends."
Translation:Jag lägger till nya vänner.
To my recollection many Finn-Swedes use the word 'kompis' instead on 'vän' when discussing friends, but this sentence does not approve kompis. Is there a slightly different meaning to the word, that I am not aware of, or does Duolingo simply not recognize it? Or is it more of a Finn-Swede thing?
Lägga till and tillägger both mean add, but in different senses that don't overlap completely. Lägga till is more like what you do when you actually add something to something, while tillägga is more adding in the sense of expanding, supplementing or going further.
Also, tillägga is a little more abstract. You might say "Vidare skulle jag vilja tillägga att..." to start a sentence in a series of reasoning clauses, to say "Furthermore, I'd like to add that..." for example. Lägga till on the other hand is a bit more concrete, not in the sense that it deals with concrete objects, but in the sense that adding something to a list would for example use lägga till.
Although the difference is a bit tricky, I hope that helps a little. I suppose there's also an element to it of me just natively knowing when it sounds wrong or when it doesn't.
But isn't it better to say "Jag sätter till nya vänner" if somebody for instance were adding them to things like carrots and potatoes? And is there a better way of saying 'witch's cauldron' than 'häxans kittel'? I just do a fair amount of cooking, is all. So I wonder. I don't even have any friends, längre, i alla fall.