This was discovered by manually inspecting the localized strings embedded inside MonochromePublic.apk.

The Android resource string identified by the name cast_intro_overlay_button_text and defined in [1] doesn't have proper localizations, i.e.:

  - The resources.arsc does *not* contain a value for the (default)
    config for this named resource. Even though it is defined
    in the corresponding res/values/strings.xml file [2]

    Note that it provides a value for en-GB (British English) though,
    but not for en-US, which is the default on Android!

  - The value is all translations, as found in resources.arsc is
    otherwise "@android:string/ok", except for the Farsi locale (fa)
    where it is "\u202A@android:string/ok". Note that \u202A
    corresponds to the right-to-left directional indicator.

  - "@android:string/ok" looks like a resource reference, which are
    normally not supported in Android string resources (but can be
    used as attribute values for other XML elements though).

Note that no other resource string in the APK has any missing default value, or uses string references.

Likely reason for the current behaviour:

  - aapt rejected the string reference for some reason for the
    default config, but not the translations?

  - a build or packaging error from the upstream 
    com.google.android.gms.play_services.cast_framework library?


[1] https://cs.chromium.org/chromium/src/out/android-Debug/gen/third_party/android_deps/com_google_android_gms_play_services_cast_framework_java/res/

[2] https://cs.chromium.org/chromium/src/out/android-Debug/gen/third_party/android_deps/com_google_android_gms_play_services_cast_framework_java/res/values/values.xml?rcl=56b8e8078938e9c3175b5a07de9130846bdd14ee&l=109