I'm running an english Windows 10 Pro (20H2). Everything but the currency etc format is set to US-English.
Still, some games (i.e. Blaston, Loop Hero) and some apps (i.e. some, but not all installers) launch in german (I am in germany). This is absolutely maddening, especially when the app or game does not have a language selection.

Is there any additional section where language is determined?
Apps and games sometimes launch in the wrong language-2021-05-01-00_50_11-start.png
Apps and games sometimes launch in the wrong language-2021-05-01-00_49_43-start.png
Apps and games sometimes launch in the wrong language-2021-05-01-00_49_30-start.png

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Solution found, but it's headache inducing:
Some apps and games ignore ALL the language settings and preferences, and for some reason look exclusively at the regional FORMAT settings. Setting this to "English (Germany)" and then manually editing the wrong parts (date is seperated with slashes instead of dots, for some reason) seems to finally solve this.