I made some tests and changed the simulator to english and region to USA.
For the share sheet, it was mixed german with english, but Camera and Safari (WebBrowser) Buttons were english. Switching back to german, everything was german without any mixed language strings.
(using ios.infoPlist)
"CFBundleAllowMixedLocalizations": true,
"CFBundleDevelopmentRegion": "de",
For my case, it is totally fine, since the case before was that all UI-Buttons have been english (only WebBrower was reflecting the correct language strings) no matter what I’ve done or set as system language. Now, mostly all text is set to the users iPhone settings with few exeptions (share sheet). I can live with that.
!