Hi Gilberto,
There is no iOS library for AdWords API. Java should work for Android, but if it doesn't, you can request help on this forum. Another probable option would be to use Xamarin's mono + AdWords API .NET library to do cross-platform development for both iOS and Android.
That said, I would recommend against making API calls directly from a mobile device to AdWords API. AdWords API is very heavy in terms of data retrieved (e.g. a 500MB report is not uncommon depending on the account size and date range), and it would drain the battery and storage of the mobile device pretty fast. The user would also incur significant data costs in such cases. My recommendation would be to build the AdWords API logic on a server, and have the mobile device talk to that service to retrieve the processed data.
Cheers,
Anash P. Oommen,
AdWords API Advisor.