Simple internationalization (i18n) package for Dart and Flutter.
Supports:
- Flutter, hot reload included
- AngularDart
- deferred loading of translations
- social distancing
- null safety
Turn this YAML file:
lib/exampleMessages.i69n.yaml
button:
save: Save
load: Load
users:
welcome(String name): "Hello $name!"
logout: Logout
Into these generated Dart classes:
class ExampleMessages {
const ExampleMessages();
ButtonExampleMessages get button => ButtonExampleMessages(this);
UsersExampleMessages get users => UsersExampleMessages(this);
}
class ButtonExampleMessages {
final ExampleMessages _parent;
const ButtonExampleMessages(this._parent);
String get save => "Save";
String get load => "Load";
}
class UsersExampleMessages {
final ExampleMessages _parent;
const UsersExampleMessages(this._parent);
String get logout => "Logout";
String welcome(String name) => "Hello $name!";
}
... and use them in your code - plain and simple.
ExampleMessages m = ExampleMessages();
print(m.users.welcome('World'));
// outputs: Hello World!
Package is an extension (custom builder) for build_runner (Dart standard for source generation) and it can be used with Flutter, AngularDart or any other type of Dart project.
- The official Dart/Flutter approach to i18n seems to be ... 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 shouldn't be just some arbitrary String, it should be a getter method!
- And if the message takes some parameters, it should be a method which take those parameters!
Create YAML file with your messages, for example:
lib/messages/foo.i69n.yaml
generic:
done: Done
ok: OK
invoice:
create: Create an invoice
delete: Delete this invoice
Add translations for different languages:
lib/messages/foo_cs.i69n.yaml (_cs = Czech translation)
generic:
done: Hotovo
# ok is the same and Foo_cs extends Foo.
invoice:
create: Vytvořit fakturu
delete: Smazat fakturu
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 --delete-conflicting-outputs
... and keep it running. Your message classes will appear next to YAML files and will be rebuilt automatically each time you change the source YAML.
For one-time (re)build of your messages run:
flutter packages pub run build_runner build --delete-conflicting-outputs
Import generated messages and use them:
import 'packages:my_app/messages/foo.i69n.dart'
...
Foo m = Foo();
return Text(m.bar);
...
... or ...
import 'packages:my_app/messages/foo_cs.i69n.dart'
Foo m = Foo_cs(); // Notice: Foo_cs extends Foo
return Text(m.bar);
You are using webdev tool already, so you just need to add i69n
as a dependency and that's all.
The implementation is VERY straightforward, which allows you to do all sorts 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 ${_apples(cnt)}.";
}
See how you can reuse the pluralization of _apples(int cnt)? (!!!)
There are three functions you can use in your message:
String _plural(int count, {String zero, String one, String two, String few, String many, String other})
String _cardinal(int count, {String zero, String one, String two, String few, String many, String other})
String _ordinal(int count, {String zero, String one, String two, String few, String many, String other})
_plural and _cardinal do the same. I just felt that _plural
sounds a little bit less scary and in most cases that's the one you need.
We need only two forms of the word "apple" in English. "Apple" (one) and "apples" (many). But in Czech, we need three:
apples:
_apples(int cnt): "${_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
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.
You might need to support multiple regions for one language. Use common locale names as file suffixes:
messages.i69n.yaml
messages.en_US.i69n.yaml
messages.en_GB.i69n.yaml
It's still useful to access your messages using the String keys in some cases. For example when the key of the message is composed dynamically at runtime, maybe like this:
var vehicleTypeMessageKey = "VehicleType.${data['type']'}";
You can access your messages like this:
print('Static: ${m.generic.ok}');
print('Dynamic: ${m.generic['ok']}');
print('Or even: ${m['generic.ok']}');
In case the key doesn't exist, an exception is thrown:
...
throw Exception('Message $key doesn\'t exist in $this');
You can disable this behaviour by adding flag 'nothrow':
_i69n: nothrow
generic:
done: Done
ok: OK
This flag is inherited to the lower levels of messages structure.
In some rare cases you might want to 'disable' this map generation (maybe to enable better tree-shaking of unused messages?). In such case use a simple flag 'nomap':
generic:
_i69n: nomap
done: Done
ok: OK
No message in 'generic' message group will be accessible through the [] operator. Scope of the flag is very narrow - one message object
in one file. Flag is not inherited into lower levels of messages and in
most cases you want to repeat it in all translations files to make an impact.
i69n uses double quotes in generated source files. Unless you need to use double quotes in your string, you should be fine.
message: Let's go!
...
String get message => "Let's go!";
Only "\t", "\r" and "\n" characters are automatically escaped by i69n.
message: "Let's\ngo!" // quotes needed by YAML, \n is converted to new line by YAML
...
String get message => "Let's\ngo!"; // new line escaped by i69n -> result is the same string
If you need to disable escaping, use "noescape" flag.
_i69n: noescape
message: Let's go!
These are a few examples of more complicated strings in which you might need to add a backslash here and there:
problematic: "Hello \\\"world\\\"!"
// ^^^ yes, tripple backslash
lessProblematic: 'Hello \"world\"!'
// ^ use single quotes in YAML, add only one backslash for Dart
alsoProblematic(int count): "${_plural(count, zero:'didn\\'t find any tasks', other: 'found some tasks')}"
// ^ here
Please prefer single quotes inside pluralization functions.
But in most cases you will be fine. Just observe generated classes and maybe experiment a little bit.
So far only 'noescape' and 'nomap'. If you need both, separate them with comma.
_i69n: noescape,nomap
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: tomucha@gmail.com
The default file (the one without language code in the file name) is supposed to be in English (meaning English locales are used in pluralization functions). You can change that by adding a 'language' to the file:
_i69n_language: de
generic:
done: Erledigt
ok: OK
The '_i69n_language' flag is only meaningful on the first line of the default file, there is no reason to use it anywhere else.
It might be usefull to teach your message objects some tyep control, for example:
friends:
michael:
name: Michael Friend
description: My good friend.
eva:
name: Eva Friend
description: My not so good friend.
It's obvious that 'friends' should implement some kind of interface so you can work with them in a type-safe way. You can achieve that by adding a 'implements' flag:
friends:
michael:
_i69n_implements: MyFriendInterface
name: Michael Friend
description: My good friend.
eva:
_i69n_implements: MyFriendInterface
name: Eva Friend
description: My not so good friend.
In most case it should be enough to add 'implements' flag in the default messages file only. And you will probably need to import that interface. Just put 'import' flag at the beginning of the file:
_i69n_import: package:my_app/my_friend_interface.dart
And you can use the import flag to import any other file (for example with some kind of number formatting). Separate multiple imports by comma.
_i69n_import: package:my_app/my_friend_interface.dart,package:my_app/my_number_formatting.dart
See example. Clone the package repository (https://github.com/fnx-io/i69n) and run:
webdev serve example:8080
or
dart run build_runner serve example:8080
Now open the browser http://localhost:8080/ and watch the dev tools console.
Created by https://fnx.io.