"¿No encuentras tu diccionario?"
Translation:You can't find your dictionary?
No, sometimes it's built in to the present tense.
No encuentro mis llaves. I can't find my keys.
¿Te ayudo, abuelito? Can I help you, Grandpa?
¿Me traes un café? Can you bring me a coffee?
The new sentences seem to be stressing that.
The more literal translation: Aren't you finding your dictionary? seems awkward.
I'm not sure why "You didn't find your dictionary?" isn't a correct translation. And, to my ear, it sounds perfectly natural in English.
That's what I put too, but I think maybe that sounds too much like past tense. If they didn't find their dictionary, that sounds like they've finished looking. If they can't find their dictionary, maybe they're still looking but haven't had any luck so far.
"You do not find your dictionary?" or "You aren't finding your dictionary?" seem like more accurate translations.
Just that the 'things' you gave are not questions! Get real, read your Grammar!