Document Reader SDK supports localization using standard iOS System Settings. If a language is required by your application but is not supported by the SDK, or you want to change our localized strings, you can add localized strings to the additional resource files and allow the SDK to be presented to users in their required system locale. You can have a look at the example of how we implemented this in our demo application in the App Store.
Go to Menu -> Settings -> Advanced -> Language.
For additional information on how you can localize your iOS Application, please see the official Apple Documentation.
Also, you can find more detailed information about the localization procedure in the documentation for developers on this link.