To make .resx work, you need to add the Microsoft.NETCore.Portable.Compatibility NuGet package. However, after that there are other problems with the construction. This is already a known issue, and people at Microsoft are working on it. I will update this message as soon as I get updates from them.
(Dec '16)
Xamarin .NET Standard Microsoft. , - , .
( '17)
, , Visual Studio 2017.