I was reading the iOS 8 series from RayWenderlich.com website.
I came to the localization and internationalization. Read every single bit of it but I could not succeed on localizing images. (I did localized strings with no errors :) )
Here is what I have done: 1- Created a project of Single View Application
2- Placed an UIImageView on the Sotryboard by drag and drop.
3- Added my image to my project (back.png).
4- Assigned my UIImageView to that image (back.png).
Now is the steps for localization:
1- Go to project navigator and select the project.
2- Under localization, "Use Base Internationalization" us checked by default.
3- I added Arabic language.
4- Localized Storyboard files and its .strings and my image (back.png)
I have two image files English and Arabic versions. Each file on its respective folder. See screenshot.

When I run my app on the simulator which has Arabic language installed and selected. My imageView still displays the English version of the image.
I tried to use ar_SA (Arabic, Saudi Arabia) but still same issue. My image is displayed in English.
I have my simulator reset, and I have deleted derived files form library/dev.../xcode... But my app does not care about the Arabic version of the image.