Translation:We go to that river, to which this bus goes.
Does this sentence sound as awkward in Hungarian as it does in English? I really want to know that. There are so many things wrong with the English, and I do not want to be learning Hungarian that sounds this bad!
In English, I might say, "We go to that river, to which this bus ALSO goes." Without the word "also," the sentence sounds a bit redundant, because we've already identified the river (with "that") - we don't need to identify it again by saying that's the river where the bus goes. It's true that someone might also want to know that the bus goes there, which is why I suggested adding "also."
Or, I might say, "We go to the river to which this bus goes." No comma, and "the" instead of "that." That way, the river is identified only once.
The best construction would probably be, "We're going to the river that this bus goes to."
It is a very badly translated sentence indeed. The Hungarian sentence is natural enough, the problem is with the translation ("We go to that river, to which this bus goes."). This is quite a literal, and very bad, translation.
The correct way would be what you guessed, without "that" and without the comma. :)
The problem lies in the logical difference between English and Hungarian. These constructions are clearly built differently in the two languages. Somebody (or some software) clearly missed that point when doing the translations.
They are different, but they're not extremely different. Both use "the... which..." in that order. So the clauses are placed in the same parts of the sentences in both languages. But they are connected differently. It seems like the rules for doing this in Hungarian are a bit more strict.
Or simply different. :)
The point is, the river is identified by the bus going there. So we are not pointing at the river ("that river") but, rather, identifying it by "that which the bus goes to". Whatever way is the most natural in English. I like your version:
"We're going to the river that this bus goes to."
But for this same thing Hungarian uses "ahhoz ..., amelyikhez ... ". The "ahhoz" indicates that an identification will follow, and the "amelyikhez" clause does the actual identification.
Yes, that is pretty much what I am saying. Hungarian usually requires the "ahhoz" part, it can't just be omitted like in English.
Without it, it would turn into a "non-identifying" sentence. We are going to the river and, btw, this bus goes to said river. But then you need "amely", not "amelyik":
"A folyóhoz megyünk, amelyhez ez a busz megy."