The two sentences have the same meaning, but different grammer. In the first tomorrow is the subject of the sentence but in the second my birthday is the subject. Sometimes two English sentences with the same meaning butdifferent grammar translate to the same Italian sentence but a lot of the time they don't.
In this case the two sentences would translate as: "Domani è il mio compleanno" and "Il mio compleanno è domani". Duolingo shouldn't accept "My birthday is tomorrow" as correct for "Domani è il mio compleanno" because there is a more accurate way to translate "My birthday is tomorrow" into Italian.
"Hey, when's your birthday?" "My birthday is tomorrow" "Hey, is something important happening tomorrow?" "Yes, tomorrow is my birthday"
Well, I see differences but not really big ones. Maybe you should just try to translate things as they're writting in Italian for the sake of ease
Crazy thing is you only get one birthday and that being the day you exit the uterus. All subsequent are anniversaries. Of course if you come back after being pronounced dead (medical or legal), you could have more than one... uhm?? Please: Philosophers, Legal experts for opinions.. 8Jun18
Io isn't used in il mio compleanno or anywhere in this sentence. I also don't understand what you mean by 'family situations' Are you referring to when you use possessives when talking about close family (singular) when you leave the definite article out like mio madre rather than il mio madre?