Mainly, I want to be able to handle multiple languages and dynamic strings (interpolation).
As a big plus, currency conversion.
At Evolve 2014, Craig Dunn presented a session on localization that might be of help. Go to the Evolve 2014 Training Videos on the Xamarin University site, and look under Xamarin.Forms or All Tracks for "Localization"
If you want to handle languages, and your app isn't too hefty, you could use a Dictionary<int, string>, and then swap out the languages through a method of some sort. This may take a little bit of time to set up the languages but it's a good straightforward plan for language support.
If you are using Visual Studio as your dev environment you can also look into the Microsoft Multilingual App Toolkit - http://blogs.msdn.com/b/matdev/ . I've used this in previous Xamarin apps and it has worked well ( your mileage may vary ).
It is a Visual Studio extension that works at build time to create localized resource files. It's probably more appropriate if you are doing pretty heavy localization and potentially outsourcing the translations of resource files to third parties. It has tooling around the translation workflow.
Just noticed there was a session on Multilingual App Toolkit at Build 2015 - http://channel9.msdn.com/Events/Build/2015/2-90
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