.NET Framework 4.8 WPF - Setting MainWindow.Language may cause app not displaying

_This issue has been moved from [a ticket on Developer Community](https://developercommunity2.visualstudio.com/t/NET-Framework-48-WPF---Setting-MainWin/833881)._

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I'm building a .NET Framework 4.8 WPF app. I have this code in the main window `Loaded` event,

`this. Language = System.Windows.Markup.XmlLanguage.GetLanguage(System.Threading.Thread.CurrentThread.CurrentUICulture.IetfLanguageTag);`

and on certain PCs/laptops (it doesn't happen on all PCs), the app will run and the main window displayed fine on the first run. If I exit the app and re-run the app, the main window will not appear anymore but the app is running (from Task Manager). Terminating and re-running it won't resolve the issue. The only possible workaround is to restart Windows and then the app main window will be displayed again.

If I remove the line stated above, everything works fine.

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### Original Comments

#### Feedback Bot on 11/26/2019, 05:01 PM:

We have directed your feedback to the appropriate engineering team for further evaluation. The team will review the feedback and notify you about the next steps.

#### Feedback Bot on 1/3/2020, 09:36 AM:

I have detected that for the last 35 days, this issue didn't have much product team activity and a very small amount of new votes or comments. Based on this, its severity, and affected area, it’s my experience that this issue is very unlikely to be fixed.

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### Original Solutions
(no solutions)