Internationalization
====================

Internationalization (I18N) refers to the process of designing a software application so that it can be adapted to
various languages and regions without engineering changes. For Web applications, this is of particular importance
because the potential users may be worldwide.

Locale and Language
-------------------

There are two languages defined in Yii application: [[\yii\base\Application::$sourceLanguage|source language]] and
[[\yii\base\Application::$language|target language]].

Source language is the language original application messages are written in such as:

```php
echo \Yii::t('app', 'I am a message!');
```

> **Tip**: Default is English and it's not recommended to change it. The reason is that it's easier to find people translating from
> English to any language than from non-English to non-English.

Target language is what's currently used. It's defined in application configuration like the following:

```php
// ...
return array(
	'id' => 'applicationID',
	'basePath' => dirname(__DIR__),
	'language' => 'ru_RU' // ← here!
```

Later you can easily change it in runtime:

```php
\Yii::$app->language = 'zh_CN';
```

Basic message translation
-------------------------

### Strings translation

Yii basic message translation that works without additional PHP extension and


### Named placeholders

```php
$username = 'Alexander';
echo \Yii::t('app', 'Hello, {username}!', array(
	'username' => $username,
));
```

### Positional placeholders

```php
$sum = 42;
echo \Yii::t('app', 'Balance: {0}', $sum);
```

> **Tip**: When messages are extracted and passed to translator, he sees strings only. For the code above extracted message will be
> "Balance: {0}". It's not recommended to use positional placeholders except when there's only one and message context is
> clear as above.

Advanced placeholder formatting
-------------------------------

In order to use advanced features you need to install and enable [intl](http://www.php.net/manual/en/intro.intl.php) PHP
extension. After installing and enabling it you will be able to use extended syntax for placeholders. Either short form
`{placeholderName, argumentType}` that means default setting or full form `{placeholderName, argumentType, argumentStyle}`
that allows you to specify formatting style.

Full reference is [available at ICU website](http://icu-project.org/apiref/icu4c/classMessageFormat.html) but since it's
a bit crypric we have our own reference below.

### Numbers

```php
$sum = 42;
echo \Yii::t('app', 'Balance: {0, number}', $sum);
```

You can specify one of the built-in styles (`integer`, `currency`, `percent`):

```php
$sum = 42;
echo \Yii::t('app', 'Balance: {0, number, currency}', $sum);
```

Or specify custom pattern:

```php
$sum = 42;
echo \Yii::t('app', 'Balance: {0, number, ,000,000000}', $sum);
```

[Formatting reference](http://icu-project.org/apiref/icu4c/classicu_1_1DecimalFormat.html).

### Dates

```php
echo \Yii::t('app', 'Today is {0, date}', time());
```

Built in formats (`short`, `medium`, `long`, `full`):

```php
echo \Yii::t('app', 'Today is {0, date, short}', time());
```

Custom pattern:

```php
echo \Yii::t('app', 'Today is {0, date, YYYY-MM-dd}', time());
```

[Formatting reference](http://icu-project.org/apiref/icu4c/classicu_1_1SimpleDateFormat.html).

### Time

```php
echo \Yii::t('app', 'It is {0, time}', time());
```

Built in formats (`short`, `medium`, `long`, `full`):

```php
echo \Yii::t('app', 'It is {0, time, short}', time());
```

Custom pattern:

```php
echo \Yii::t('app', 'It is {0, date, HH:mm}', time());
```

[Formatting reference](http://icu-project.org/apiref/icu4c/classicu_1_1SimpleDateFormat.html).


### Spellout

```php
echo \Yii::t('app', '{n,number} is spelled as {n, spellout}', array(
	'n' => 42,
));
```

### Ordinal

```php
echo \Yii::t('app', 'You are {n, ordinal} visitor here!', array(
	'n' => 42,
));
```

Will produce "You are 42nd visitor here!".

### Duration


```php
echo \Yii::t('app', 'You are here for {n, duration} already!', array(
	'n' => 42,
));
```

Will produce "You are here for 47 sec. already!".

### Plurals

Different languages have different ways to inflect plurals. Some rules are very complex so it's very handy that this
functionality is provided without the need to specify inflection rule. Instead it only requires your input of inflected
word in certain situations.

```php
echo \Yii::t('app', 'There {n, plural, =0{are no cats} =1{is one cat} other{are # cats}}!', array(
	'n' => 0,
));
```

Will give us "There are no cats!".

In the plural rule arguments above `=0` means exactly zero, `=1` stands for exactly one `other` is for any other number.
`#` is replaced with the `n` argument value. It's not that simple for languages other than English. Here's an example
for Russian:

```
Здесь {n, plural, =0{котов нет} =1{есть один кот} one{# кот} few{# кота} many{# котов} other{# кота}}!
```

In the above it worth mentioning that `=1` matches exactly `n = 1` while `one` matches `21` or `101`.

To learn which inflection forms you should specify for your language you can referer to
[rules reference at unicode.org](http://unicode.org/repos/cldr-tmp/trunk/diff/supplemental/language_plural_rules.html).

### Selections

You can select phrases based on keywords. The pattern in this case specifies how to map keywords to phrases and
provides a default phrase.

```php
echo \Yii::t('app', '{name} is {gender} and {gender, select, female{she} male{he} other{it}} loves Yii!', array(
	'name' => 'Snoopy',
	'gender' => 'dog',
));
```

Will produce "Snoopy is dog and it loves Yii!".

In the expression `female` and `male` are possible values. `other` handler values that do not match. Strings inside
brackets are sub-expressions so could be just a string or a string with more placeholders.

Formatters
----------

In order to use formatters you need to install and enable [intl](http://www.php.net/manual/en/intro.intl.php) PHP
extension.
