Created attachment 151558 [details]
Contains 3 files. AuthDialog displays the problem, the others are relevant settings.

SUMMARY
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Open Discover and select any software. Press Install button. An authorization dialog appears. In my system, i have selected English language but the Region and Formats are set in my native language. Part of the text that appears in the authorization dialog is in my native language instead of English.
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STEPS TO REPRODUCE
1. Open Discover and select any software. 
2. Press Install button.

OBSERVED RESULT
Notice the text that appears in the Authorization dialog that opens. Part of it is in the user's native language (image KDE_AuthDialog in the attached ZIP file).

EXPECTED RESULT
All of the text that appears in the Authorization dialog should be in the system language.


SOFTWARE/OS VERSIONS
Windows: 
macOS: 
Linux/KDE Plasma: 
(available in About System)
KDE Plasma Version: 
KDE Frameworks Version: 
Qt Version: 

ADDITIONAL INFORMATION
Using latest KDE Neon distribution, fully updated. In the past, i have experienced this behavior though in other flavors (Kubuntu, KDE Mint [when it was around] and Fedora).