I noticed that there was the same question posted in our ticketing system with an attached project, but from another account. I already answered the question there (in ticket with ID:929908), however, I will also quote myself in this forum because the answer can be helpful to someone else with a similar case.
"The resources are not apply because the new LocalizationManager needs to be defined before the create of the application's UI. For example, you can add it just before the InitializeComponent() method. "
LocalizationManager.Manager = new LocalizationManager()
ResourceManager = Resource1.ResourceManager
In addition you can take a look at the Localization