ASP.NET Core (.NET Framework) and Localization

Why the libraries that I'm using in my ASP.NET Core project (.NET Framework) do not return messages translated as the selected culture?

For example:

ResourceManager rm = new ResourceManager(typeof(ClassLibrary1.Test));
string test1 = rm.GetString("Hello", new System.Globalization.CultureInfo("en-US"));
string test2 = rm.GetString("Hello", new System.Globalization.CultureInfo("pt-BR"));

This code is in a library part that has business rules and returns a message.

But when it is referenced in an ASP.NET MVC project it returns the message as the current culture (pt-br, en-us).

But if this library is referenced in a ASP.NET Core project (.NET Framework), nothing makes it return in the current culture.

ASP.NET

ResourceManager rm = new ResourceManager(typeof (ClassLibrary1.Test));
string test1 = rm.GetString("Hello", new System.Globalization.CultureInfo("en-US"));
string test2 = rm.GetString("Hello", new System.Globalization.CultureInfo("pt-BR"));

test1 = Message en-US
test2 = Message pt-BR


ASP.NET Core

ResourceManager rm = new ResourceManager(typeof(ClassLibrary1.Test));
string test1 = rm.GetString("Hello", new System.Globalization.CultureInfo("en-US"));
string test2 = rm.GetString("Hello", new System.Globalization.CultureInfo("pt-BR"));

test1 = Message pt-BR
test2 = Message pt-BR


Detail that everything is configured correctly on ASP.NET Core because:

IStringLocalizer <HomeController>
@Inject IViewLocalizer localizer

It works perfectly.

The problem is in the Resources of the referenced libraries.

Can someone help me?