Merge in the flutter gallery (#176)

gallery/gallery/lib/l10n/README.md

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+# Localization
+
+## Generating New Locale Messages
+
+When adding new strings to be localized, update `intl_en_US.arb`, which
+is used by this project as the template. When creating new entries, they
+have to be in the following format:
+
+```arb
+  "dartGetterVariableName": "english translation of the message",
+  "@dartGetterVariableName": {
+    "description": "description that the localizations delegate will use."
+  },
+```
+
+In this example, `dartGetterVariableName` should be the Dart method/property
+name that you will be using in your localizations delegate.
+
+After adding the new message in `intl_en_US.arb`, it can be used in the app by
+regenerating the GalleryLocalizations delegate and the `messages_*.dart` files.
+This allows use of the English message through your localizations delegate in
+the application code immediately without having to wait for the translations
+to be completed.
+
+To generate `GalleryLocalizations`, from `gallery/` run:
+```
+make l10n
+```
+
+For more details on what `make l10n` runs, you can read below under Generate GalleryLocalizations.
+
+The current supported locales list is sorted alphabetically. So after running the script, update
+`gallery_localizations.dart` to move the `en_US` locale to the top of the list.
+
+## Generate GalleryLocalizations
+To generate GalleryLocalizations, from `gallery/` run:
+
+```dart
+dart ${YOUR_FLUTTER_PATH}/dev/tools/localization/bin/gen_l10n.dart \
+    --template-arb-file=intl_en_US.arb \
+    --output-localization-file=gallery_localizations.dart \
+    --output-class=GalleryLocalizations
+```
+
+From `gallery/`, run `dart ../l10n_cli/bin/main.dart`, which will generate
+`intl_en_US.xml`. This will be used by the internal translation console to
+generate messages in the different locales.
+
+Run the formatter to make the Flutter analyzer happy:
+```
+flutter format .
+```
+
+## Generating New Locale Arb Files
+
+Use the internal tool to create the `intl_<locale>.arb` files once the
+translations are ready.
+
+## Generating Flutter Localization Files
+
+If new translations are ready and the `intl_<locale>.arb` files are already
+available, run the following commands to generate all necessary
+`messages_<locale>.dart` files and the `localizations_delegate.dart` file:
+
+```
+make gen-l10n
+make format
+```
+
+which is equal to
+
+```dart
+dart ${YOUR_FLUTTER_PATH}/dev/tools/localization/bin/gen_l10n.dart \
+    --template-arb-file=intl_en_US.arb \
+    --output-localization-file=gallery_localizations.dart \
+    --output-class=GalleryLocalizations
+
+flutter format .
+```
+
+This ensures the generated `.dart` files updated with the latest translations.
+
+Run the formatter to make the Flutter analyzer happy:
+```
+flutter format .
+```
+