"I am waiting for you."
Translation:Jag väntar på dig.
It's "dig" because it's in accusative. I see you're doing German and Spanish; it's like "ich warte auf dich" rather than "ich warte auf du", or "yo te espero" rather than "yo tú espero".
As for "på", that's just the preposition Swedish uses when waiting for somebody.
väntar på just means waiting in general, but inväntar means that you're waiting for something or somebody, and then something else happens.
For instance, you could both vänta på or invänta some test results, but if you use inväntar, it would imply that you're e.g. waiting for the results so you can make some decision.
Sorry about that, I was just making an observation for all of the people who might be curious about the different ways of reasonably translating the sentence. I love learning Nordic languages because it gives me a deeper appreciation for English and its myriad (often archaic sounding) dialects. Have a lingot, on me!