// Surrogate
[ProtoContract]
public class SurrogateCultureInfo
{
    [ProtoMember(1)]
    public string Culture { get; set; }

    public static implicit operator SurrogateCultureInfo( CultureInfo info )
    {
        return
            info != null
            ? new SurrogateCultureInfo { Culture = info.Name }
            : null;
    }

    public static implicit operator CultureInfo( SurrogateCultureInfo surrogate )
    {
        CultureInfo info = new CultureInfo(surrogate.Culture);

        return info;
    }
}

// Setting the surrogate
var model = ProtoBuf.Meta.TypeModel.Create();
AddTypeToModel<CultureInfo>( model ).SetSurrogate( typeof( Surrogates.SurrogateCultureInfo ) );

private static MetaType AddTypeToModel<T>( RuntimeTypeModel typeModel )
{
    var properties = typeof(T).GetProperties().Select(p => p.Name).OrderBy(name => name);

    return typeModel.Add(typeof(T), true).Add(properties.ToArray());
}