Yes, you can say or write 'the,' if that's your question.

the twelfth /12th of February (AE/BE, written or spoken)

12 February (written BE)
February 12 (written AE, spoken as "February twelfth")

In AE, we do read dates written with slashes, which is a kind of shorthand, simply as numbers, not as ordinals. 'Nine/thirty' means 9/30 -- which of course would be 30.9. in German. (How would you speak that? Den dreißigsten des neunten?)

There are countless threads in the forum archive on similar questions, but somehow I never can remember the BE and the German if I haven't actually heard them much in real life. It's funny that this seems to be an area that textbooks and dictionaries don't always cover. Maybe modern language courses like the ones on LEO do.

Re #3: That's generally true in a full date that includes the year. But the version the original poster asks about, e.g., 'the twelfth /12th of February,' is fine without the year.

AE: the Fourth of July
BE: Remember, remember, the Fifth of November ...

Ich danke euch allen, ganz besonders hm-us für die gut strukturierte Antwort!