"Jadę za granicę."
Translation:I am going abroad.
I am going across the border
I am going across the lines
those two sentences have been translated into Jade za granice in Songs, Films and Books
So you'd still say this if your country (or the one you were going to) was an island? Or if you were going by plane or boat otherwise?
You can specify, especially if the vehicle is of importance, but "jadę" is perfectly fine even if you go by plane/boat.
Oh ok. That's interesting, thank you. I was actually asking about the 'za granicę' part - that is, would you still use this phrase even if your journey abroad didn't involve physically crossing a border?
Yes, definitely. You can either say that or just specify the country, I don't think there's any other natural way.
Besides, even if you're going by plane, one could argue that you still cross at least one border, just not a border passage ;)
"I go abroad" is the wrong tense in English. "I go abroad" doesn't mean you're doing it now, it means you regularly go abroad (and are not currently doing so).
^^ present continuous is needed to show the action happens now. "I am going"
It seems like sometimes za is followed by an accusative-form noun and sometimes instrumental. Is there a way to predict which it will be? It seems like za as in "behind" is usually instrumental? Have any great links for prepositions and cases?
Not only 'za', but some other prepositions behave this way.
Using Instrumental denotes location, something simply is located behind X.
Using Accusative denotes movement, something moves/is moved to end up behind X.
You may check this post by alukasiak, one of the course creators: https://www.clozemaster.com/blog/polish-prepositions/ - as well as check his other posts on this website.