|I do agree that "no worries" and "not a problem" are very poor substitutes for "You're welcome."
But..."you're welcome" to what, exactly? (You're welcome to my generosity, I guess?) As opposed to saying that whatever task is being thanked for was "not a problem" to do? Why is that a "poor substitute" for anything? (Is it actually even a substitute? Was "you're welcome" always the expected idiom?) As was already stated, in Spanish, the idiom is indeed "it was nothing (to do this for you)" - I think that's a very valid response.
I like the Italian response, "prego" - literally, "I pray," or more colloquially, "I wish you well." A very congenial way to respond to being thanked, I think.