resConfigs per build type

For some reason the individual buildType configs doesn't support the resConfigs command as you point out, but defaultConfig does and then you can use this trick to manipulate it per build type even without flavors configured:

android {
    defaultConfig {
        resConfigs "en"
    }
    applicationVariants.all { variant ->
        if (variant.buildType.name.equals("debug")) {
            variant.mergedFlavor.resourceConfigurations.add("de")
        }
    }
}