Guys, I'm working on a mobile campaign and was wondering if you guys create
the banners in your target country's language, or English banner that points to
a foreign language landing page (the offer).
I'm not sure if it's a better idea to translate the banners or use
English on them as I do for regular campaigns in the US/UK, etc...
Any help would be greatly appreciated.
The general consensus is that banners and LPs in native language will USUALLY perform better than english creatives. Please note that this is not true in 100% cases.
A very important thing is that the translation is flawless - grammatically incorrect translation or just a poor translation will hurt the conversions and it can end up worse than english copy in the first place.
There are also GEOs where english simply works better than native language - for example because there are several languages spoken.
Sometimes english works better due to the nature of the ad - system messages in banners, generic play/download banners etc ...
The angle can work better in english than in native language - it could be slang, something hard to translate etc ...
I personally split test english copy against translated in about 80% of cases, usually a good translation wins, but I had an english banner perform better in some many times, that I simply don't risk not testing it anymore 
I don't know about you, but I tend not to click on ads where I have no clue what the text means ... just sayin'