i69n 0.0.3

Alternative i18n for Dart and Flutter, based on YAML files and source generation.

Alternative internationalization package for Dart and Flutter.

Write your messages into YAML files, and let this package generate a Dart objects from those files. Turn this YAML:

generic:
  ok: OK
  done: DONE

Into this Dart class:

class GenericMessages {
  const GenericMessages();
  String get ok => "OK";
  String get done => "DONE";
}

WARNING: Not battle tested yet! Also the documentation is rather rudimentary. It's more or less a proof of concept. But looks promising.

i69n: 51 points better than i18n!

(nice!)

Motivation

• The official Dart/Flutter approach to i18n seems ... complicated and kind of ... heavyweight.
• I would like my messages to be checked during compile time. Is that message really there?
• Key to the localized message should not be just some arbitrary String, it should be a getter method!
• And if the message takes some parameters, the method should take those parameters!
• I like to bundle messages into thematic groups, the i18n tool should support that and help me with it.
• Dart has awesome string interpolation, I want to leverage that!
• I like build_runner and code generation.
• I love the name. i69n is hilarious.

Solution

Write your messages into a YAML file:

exampleMessages.i69n.yaml (default messages):

generic:
  ok: OK
  done: DONE
invoice:
  create: Create invoice
  delete: Delete invoice

Write your translations into other YAML files:

exampleMessages_cs.i69n.yaml (_cs = Czech translation)

generic:
  done: Hotovo
invoice:
  create: Vytvořit fakturu
  delete: Smazat fakturu

... run the webdev tool, or build_runner directly, and use your messages like this:

ExampleMessages m = ExampleMessages();
print(m.generic.ok);
print(m.generic.done); // output: DONE

m = ExampleMessages_cs();
print(m.generic.done); // output: Hotovo

Parameters and pluralization

The implementation is VERY straightforward, but that allows you to do a lot of crazy stuff:

invoice:
  create: Create invoice
  delete: Delete invoice
  help: "Use this function
  to generate new invoices and stuff.
  Awesome!"
  count(int cnt): "You have created $cnt ${_plural(cnt, one:'invoice', many:'invoices')}."
apples:
  _apples(int cnt): "${_plural(cnt, one:'apple', many:'apples')}"
  count(int cnt): "You have eaten $cnt ${_apples(cnt)}."

Now see the generated classes:

class ExampleMessages {
    const ExampleMessages();
    InvoiceExampleMessages get invoice => InvoiceExampleMessages(this);        
    ApplesExampleMessages get apples => ApplesExampleMessages(this);
}
    
class InvoiceExampleMessages {
    final ExampleMessages _parent;
    const InvoiceExampleMessages(this._parent);
    String get create => "Create invoice";
    String get help => "Use this function to generate new invoices and stuff. Awesome!";
    String get delete => "Delete invoice";
    String count(int cnt) => "You have created $cnt ${_plural(cnt, one:'invoice', many:'invoices')}.";
}

class ApplesExampleMessages {
    final ExampleMessages _parent;
    const ApplesExampleMessages(this._parent);
    String _apples(int cnt) => "${_plural(cnt, one:'apple', many:'apples')}";
    String count(int cnt) => "You have eaten $cnt ${_apples(cnt)}.";
}         

See how you can reuse the pluralization of _apples(int cnt)? (nice!)

There are three functions you can use in your message:

String _plural(int count, {String zero, String one, String two, String few, String many, String other})

String _cardinal(int count, {String zero, String one, String two, String few, String many, String other})

String _ordinal(int count, {String zero, String one, String two, String few, String many, String other})

_plural and _cardinal do the same. I just felt that _plural is a little bit less scary name :-)

We need only two forms of the word apple in English. Apple and apples. But in Czech:

apples:
  _apples(int cnt): "${_plural(cnt, one:'jablko', few: 'jablka', many:'jablek')}"

See also:

• http://cldr.unicode.org/index/cldr-spec/plural-rules
• https://www.unicode.org/cldr/charts/latest/supplemental/language_plural_rules.html

Custom pluralization

The package can correctly decide between 'one', 'few', 'many', etc. only for English and Czech (for now). But you can easily plug your own language, see example/main.dart and Czech and English implementation.

If you implement support for your language, please let me know, I'll gladly embed it into the package.

How to use generated classes

How to decide what translation to use (ExampleMessages_cs?, ExampleMessages_hu?) is up to you. The package simply generates message classes, that's all.

import 'exampleMessages.i69n.dart';
import 'exampleMessages_cs.i69n.dart' deferred as cs;

void main() async {
  ExampleMessages m = ExampleMessages();
  print(m.apples.count(1));
  print(m.apples.count(2));
  print(m.apples.count(5));

  await cs.loadLibrary();
  m = cs.ExampleMessages_cs(); // see? ExampleMessages_cs extends ExampleMessages
  print(m.apples.count(1));
  print(m.apples.count(2));
  print(m.apples.count(5));

}    

Where and how to store instances of these message classes - again, up to you. I would consider ScopedModel for Flutter and registering messages instance into dependency injection in AngularDart.

But in this case a singleton would be acceptable also.

How to use with Flutter

Create YAML file with your messages, for example:

lib/messages/foo.i69n.yaml

Add build_runner as a dev_dependency and i69n as a dependency to pubspec.yaml:

dependencies:
  flutter:
    sdk: flutter
  i69n: any
  ...

dev_dependencies:
  build_runner: any
  flutter_test:
    sdk: flutter

Open a terminal and in the root of your Flutter project run:

flutter packages pub run build_runner watch

... and keep it running. Your message classes will appear next to YAML files and will be rebuild each time you change source YAML files.

For one-time rebuild of messages run:

flutter packages pub run build_runner build

Import generated messages and use them:

import 'messages/foo.i69n.dart'

...

Foo m = Foo();
print(m.bar);
...

How to use with AngularDart

You are probably using webdev tool already, so you just need to add i69n as a dependency and that's all.

TODO

• More detailed docs.
• Use it in some of our projects for real.
• Current limitation: default language must be english
• TODO: support custom imports

Example

See example. Clone the repository and run:

webdev serve example:8080

or

pub run build_runner serve example:8080

Now open the browser http://localhost:8080/ and watch the dev tools console.