How would one say that he is travelling IN Russia?
Same thing with to ---> [Αυτός ταξιδεύει/Ταξιδεύει] στη [Ρωσία/Ρωσσία]
OK, I wasn't sure whether it was correct, so I did not recommend that it should be added as a correct answer. I guess it should.
I am having trouble knowing when to use στη or στην.
You can use either.
I think it must be πρως Ρωσία instead of στη Ρωσια
It would be προς (τη) Ρωσία but προς ιs dropped in standard use because it sounds a lot more emphatic, like towards. So you just drop it. :)
I said it because we can not distinguish between travelling inside russia and travelling towards rusia
Both are accepted for the English translation.