The recommended approach is to add the keyboard for the desired language by enabling it within the Settings app. On your iPad, go to Settings app → General → Keyboard → Keyboards → Add New Keyboard..., and select the keyboard of your choice. Of late, iOS has evolved to include support for a wide variety of languages and this approach should be taken first.
The intended approach as discussed in the question is neither possible and straightforward, nor is it recommended for attempting to add support for a new language in your iPad keyboard. Also, it isn't advisable to jailbreak your iOS device just for the sake for changing keyboard language.
Additionally, starting with iOS 8, Apple has enabled support for 3rd-party keyboard apps. A lot of such apps are now available on the App Store, and you should be able to find the one that fits your requirements. Alternatively, you can also write your own keyboard app that best suits your needs.
You can Learn more about keyboard settings by reading this Apple Support article, About the keyboards settings on your iPhone, iPad, and iPod touch.