The screen which is shown inside of the "Have you been tested?" box -> "Test with QR Code" -> "Accept"
a) has an unlocalized title
~b) is only shown in German.~

Localized string ~and screen shown in the language of the app.~
Seems like this screen comes directly from iOS, if the language from the whole phone, and not only the language from the app is set to English, the screen is shown in English (but it still shows "PRE_AUTHORIZATION_TITLE").
So that it's shown in German although the app's language is English seems to be intended.
This is already addressed to Apple
On iOS 14.4.1 is the localised text.
Thanks for the feedback @thomasaugsten & @jucktnich.
Let's hope that this doesn't make it into the final release of iOS 14.5.
I'll close this issue when it's fixed by Apple.
@dsarkar
Feel free to add the apple label.