Is the addotional downloads gained by more direct exposure in the appstores or is it because users from other countries will like your app more if it is in their own language?
It highly depends on the region, but mostly the idea is the second part.
In countries like france, japan and russia, its said that they prefer localized apps a lot more.
I've heard that chinese gamers actually don't care that much.
In sweden, a localized game can make it feel more like a kids game, older players tend to think english language is "cooler".
If they need to actually read the text to understand the game and what to do, localization becomes more important.
Some app stores have prefered to promote localized apps, but that is for the above reasons, the idea that customers prefer it.
It might increase your chance for it though, but apart from that, I don't think your visibility is impacted.
I don't think anyone filters on localization.
Say for a very simple app that can be understood by anyone and with very little text.
If that is the case, localization has less impact.
But then again, if you have just a few strings to translate, localization is pretty cheap.
We actively try to keep strings to a minimum, but they have a tendency to be really hard to get fully rid of :)
Then everything isn't that easy to translate... In the latest edition of our skateboard game, we opted to translate everything but the trick names, they are in english in all regions.