NET 6, WPF App, CultureInfo.CurrentUICulture is reseted to "en-US" after programmatically set to "RU"

Question

Hi everyone!
I have such type of app:
<Project Sdk="Microsoft.NET.Sdk">
<PropertyGroup>
<OutputType>WinExe</OutputType>
<TargetFramework>net6.0-windows</TargetFramework>
<UseWPF>true</UseWPF>
</PropertyGroup>
In App.xaml.cs:
private async void OnStartup(object sender, StartupEventArgs e)
{
Host = CreateHostBuilder(e.Args).Build();

            IConfiguration configuration = Host.Services.GetRequiredService<IConfiguration>();
            string uiCultureName = configuration["UICulture"]; // "RU"
            CultureInfo.CurrentUICulture = new CultureInfo(uiCultureInfo);

            var task = Host.RunAsync();
            ...
            var mainWindow = new MainWindow();
            mainWindow.Show();

Main window shows correct resources from Resources.RU.resx, but when I click button, child window is shown using Resources.resx (English). CurrentThread.ManagedThreadI is 1 for both window constructors. But for child window CultureInfo.CurrentUICulture is “en-US”. Help please, how can I track, where is CultureInfo.CurrentUICulture reseted back to “en-US”? Thank you in advance for any help. Windows itself has English UI.

Answer 1

If you want to set the child window to display RU.resx resources. For setting up and using resources, you could try to refer to the following methods.
Project structure:

En.resx:

RU.resx:

App.xaml.cs:

public partial class App : Application  
  {  
    public App()  
    {  
      System.Threading.Thread.CurrentThread.CurrentUICulture = new System.Globalization.CultureInfo("RU");  
      System.Threading.Thread.CurrentThread.CurrentUICulture = new System.Globalization.CultureInfo("En");  
    }  
  }  

Add xmlns:res="clr-namespace:CurrentUICultureDemo.Properties" to both MainWindow.xaml and SubWindow.xaml.
MainWindow.xaml:

<Window x:Class="CurrentUICultureDemo.MainWindow"  
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"  
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"  
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"  
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"  
        xmlns:local="clr-namespace:CurrentUICultureDemo"  
        xmlns:res="clr-namespace:CurrentUICultureDemo.Properties"  
        mc:Ignorable="d"  
        Title="MainWindow" Height="450" Width="800">  
    <StackPanel>  
        <Button x:Name = "button1" Content="{x:Static res:RU.Submit}"   Width="75"/>  
        <Button x:Name="Button2" Content="{x:Static res:RU.Password}"  Width="75" Click="Button2_Click"/>  
    </StackPanel>  
</Window>  

MainWindow.xaml.cs:

public partial class MainWindow : Window  
  {  
    public MainWindow()  
    {  
      InitializeComponent();  
    }  

    private void Button2_Click(object sender, RoutedEventArgs e)  
    {  
      SubWindow w= new SubWindow();  
      w.Show();  
    }  
  }  

SubWindow.xaml:

<Window x:Class="CurrentUICultureDemo.SubWindow"  
        xmlns="http://schemas.microsoft.com/winfx/2006/xaml/presentation"  
        xmlns:x="http://schemas.microsoft.com/winfx/2006/xaml"  
        xmlns:d="http://schemas.microsoft.com/expression/blend/2008"  
        xmlns:mc="http://schemas.openxmlformats.org/markup-compatibility/2006"  
        xmlns:local="clr-namespace:CurrentUICultureDemo"  
        mc:Ignorable="d"  
         xmlns:res="clr-namespace:CurrentUICultureDemo.Properties"  
        Title="SubWindow" Height="450" Width="800">  
    <StackPanel>  
        <Button x:Name = "btn1" Content="{x:Static res:RU.Submit}"  Width="75"/>  
        <Button x:Name = "btn2" Content="{x:Static res:En.Submit}"  Width="75"/>  
        <Button x:Name="btn3" Content="{x:Static res:RU.Password}"    Height="30" Width="75"/>  
        <Button x:Name="btn4" Content="{x:Static res:En.Password}"    Height="30" Width="75"/>  
    </StackPanel>  
</Window>  

The result:

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