"Poland is by the Baltic Sea."

Translation: Polen ligger vid Östersjön.

[Sjodni]

Why is the "the" taken out of here?

[Lundgren8]

It’s the -n of sjön. Sjö means ’sea’. Note that this is pronounced with a short ö and a long n, whereas sjö has a long ö.

[Sjodni]

Oh, I didn't catch that when translating that, and put östersjöen......whoops, my mistake!

[hiro934956]

As I hear Östersjön (well, actually I could not catch it), I mistook it as "Östersund" where I once worked part-time in summer in that famous city hotel/ restaurant´s kitchen a few decades ago. I never heard of Östersjön.