How to create a multilingual project

I'm new to VB.net and I'm trying to do a simple multilingual project.

So far I've created 2 resource files:

en-US.resx  
pt-PT.resx

in both of them I have the same ID's and diferent values (strings only) (these strings will be used across multiple forms)

When I change the laguage I do:

Thread.CurrentThread.CurrentCulture = New CultureInfo("en-US")

or

Thread.CurrentThread.CurrentCulture = New CultureInfo("pt-PT")

Based on the language I want to see.

But I dont know how to access my resource files properly, Doing:

Dim assembly As System.Reflection.Assembly
assembly = Me.GetType.Assembly
Dim resourceManager As New System.Resources.ResourceManager("My.Resources", assembly)  
MsgBox(resourceManager.GetString("TEST"))  

Gives me an exception System.Resources.MissingManifestResourceException' occurred in mscorlib.dll

What am I missing?

edit after the first sugestion:

Well I just stop using the resource manager. Apparently the resource manager is not needed and now its working. I hope this helps someone else when the tutorials seem to fail :\

Public Class Form1
  Private Sub Button1_Click(sender As Object, e As EventArgs) Handles Button1.Click
    Thread.CurrentThread.CurrentUICulture = CultureInfo.GetCultureInfo("en-US")
    MsgBox(My.Resources.MStrings.TEST)
  End Sub

  Private Sub Button2_Click(sender As Object, e As EventArgs) Handles Button2.Click
    Thread.CurrentThread.CurrentUICulture = CultureInfo.GetCultureInfo("pt-PT")
    MsgBox(My.Resources.MStrings.TEST)
  End Sub
End Class