Mirko Thiessen wrote:
What do you think about that solution: call it "Oder" in articles relating to German regions (Lower Oder Valley National Park), call it "Odra" in articles relating to Polish regions (Szczecin).
Is this common practice in English?
So, my vote is to leave the main article where it is now: "Odra", since there are greater portions of the river in Poland.
The location of the river is one factor in determining what we should call it in English, but not the only factor. We know the name in Polish, and the name in German, but the question of what the name "really" is in English seems to be primarily a question of common usage.
It seems like this river is not widely talked about in English at all (based on my web searches), so it probably doesn't matter a great deal either way. :-)
--Jimbo