MissingTranslation for default language ( "..." is not translated in "en")

I don't know where the en comes from, but if I define the language of my default resources in the xml file like following

<resources
    xmlns:tools="http://schemas.android.com/tools"
    tools:locale="en">

the error disappears...

Probably, I just guess, some gradle imports have the en folder...

Maybe the build is getting confused by the string-array? It's good practice to have the array only in one values folder and define the strings as external resources. So instead of your entry, it's better to do this:

<string-array name="pause_alarms">
    <item>@string/silent</item>
    <item>@string/vibrate</item>
    ... etc ...
</string-array>

Then in res/values/strings.xml

<string name="silent">Silent</string>
<string name="vibrate">Vibrate</string>
 ... etc ...

and in res/values-de/strings.xml

<string name="silent">Leise</string>
<string name="vibrate">Vibrieren</string>
 ... etc ...

This way you don't have to keep 2 string-arrays up to date and sync'd in order, just the raw string values.

The "en" thing is weird - in the docs for localization, Google never mention English. They only ever talk about the "default" language. Makes sense, as values is language-neutral. You could write the default in Spanish and have a values-en folder, it wouldn't matter.

Other things to check - are you using local libraries in the project folder? Maybe they have resources in a values-en folder that are getting picked up and confusing the build system?