You can add supported languages in the Info.plist by adding a CFBundleLocalizations array like this:
<key>CFBundleLocalizations</key>
<array>
<string>German</string>
<string>French</string>
<string>Italian</string>
</array>
You should probably change the CFBundleDevelopmentRegion too since it uses English by default and you don’t want to support English:
<key>CFBundleDevelopmentRegion</key>
<string>de</string>