Repository: flutter
Issue: [flutter_localizations] Translations are not generated
Labels: framework,a: internationalization,f: cupertino,d: api docs,has reproducible steps,found in release: 2.5,found in release: 2.6,team-design,triaged-design

Follow the instructions from [Adding a new string to localizations](https://github.com/flutter/flutter/tree/master/packages/flutter_localizations#adding-a-new-string-to-localizations)  to add the following string in `cupertino_en.arb`. 

```console
  "closeButtonLabel": "Close",
  "@closeButtonLabel": {
    "description": "The label for close buttons."
  }
```

Step 4 mentions English text will be copied to other locales when executing `dart dev/tools/localization/bin/gen_missing_localizations.dart` then asks to re-generate with `dart dev/tools/localization/bin/gen_localizations.dart --overwrite`, yet text in other locales is not translated. 

Expected results:
`Close` is translated to other Cupertino locales

Actual results:
`Close` button is not translated in other Cupertino locales, still has English text



<details> 
<summary>flutter doctor -v</summary> 
	
```console
[✓] Flutter (Channel master, 2.6.0-12.0.pre.238, on macOS 12.0 21A5543b darwin-x64, locale en-GB)
    • Flutter version 2.6.0-12.0.pre.238 at /Users/tahatesser/Code/flutter_master
    • Upstream repository https://github.com/flutter/flutter.git
    • Framework revision bf429f2771 (33 hours ago), 2021-10-06 21:44:27 -0700
    • Engine revision e914da14f1
    • Dart version 2.15.0 (build 2.15.0-178.0.dev)

[✓] Android toolchain - develop for Android devices (Android SDK version 30.0.2)
    • Android SDK at /Users/tahatesser/Code/SDK
    • Platform android-30, build-tools 30.0.2
    • ANDROID_HOME = /Users/tahatesser/Code/SDK
    • Java binary at: /Applications/Android Studio.app/Contents/jre/Contents/Home/bin/java
    • Java version OpenJDK Runtime Environment (build 11.0.10+0-b96-7281165)
    • All Android licenses accepted.

[✓] Xcode - develop for iOS and macOS (Xcode 13.0)
    • Xcode at /Applications/Xcode.app/Contents/Developer
    • CocoaPods version 1.11.2

[✓] Chrome - develop for the web
    • Chrome at /Applications/Google Chrome.app/Contents/MacOS/Google Chrome

[✓] Android Studio (version 2020.3)
    • Android Studio at /Applications/Android Studio.app/Contents
    • Flutter plugin can be installed from:
      🔨 https://plugins.jetbrains.com/plugin/9212-flutter
    • Dart plugin can be installed from:
      🔨 https://plugins.jetbrains.com/plugin/6351-dart
    • Java version OpenJDK Runtime Environment (build 11.0.10+0-b96-7281165)

[✓] VS Code (version 1.61.0)
    • VS Code at /Applications/Visual Studio Code.app/Contents
    • Flutter extension version 3.27.0

[✓] Connected device (3 available)
    • iPhone 13 (mobile) • 18A4D720-B501-403C-A2CC-46E77B2EB618 • ios            • com.apple.CoreSimulator.SimRuntime.iOS-15-0 (simulator)
    • macOS (desktop)    • macos                                • darwin-x64     • macOS 12.0 21A5543b darwin-x64
    • Chrome (web)       • chrome                               • web-javascript • Google Chrome 94.0.4606.81

• No issues found!
```
	 
</details>