"Het regent sinds het ontbijt."
Translation:It has rained since breakfast.
No, no past tense. (1)It has rained SINCE breakfast ✒"Het regent sinds het ontbijt" or (2)I have been in love with her FOR two years ✒"Ik ben (al) twee jaar verliefd op haar" ; both cases are a regular present perfect tense, indicating that the action started in the past but is still going on at the moment the phrase is used. This isn't a past but a specific kind of present tense used with "since" or "for". The Dutch translation is in the simple present (onvoltooid tegenwoordige tijd), but the English is a present perfect structure indeed. Happy learning!
Thanks for the explanation. 'It is raining since breakfast' could be correct as well?
With "since", we can't use the present continuous (i'd say it's because it means the action has begun in the past, and not only happening now)