It would be difficult to generalize based on one's experience, when i first moved here, i had this language partner, she spoke no English, and I spoke little Chinese but given the fact that we had to communicate, i felt the urge to learn and force myself
to speak Chinese, eventually my chinese got better and better, however the relation moved from language partner to something else...
After her i have had different language partners, but most of them wanted to speak English, and oftentimes i would be speaking in Chinese, and they would be speaking in English, even if my Chinese is way better than their English, its really really annoying,
and quite frankly they have improved their language skills more than me.
What I think is if you want to find a language partner, you better go for the ones that can't speak English or speak little English and if you don't want to fall into the "Romance partner" kinda thing, then you should go for a dude, (or a girl if you gay...lol)