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. Yii offers a full spectrum of I18N features that support message translation, view translation, date and number formatting.

Locale and Language

Locale is a set of parameters that defines the user’s language, country and any special variant preferences that the user wants to see in their user interface. It is usually identified by an ID consisting of a language ID and a region ID. For example, the ID en-US stands for the locale of English and United States. For consistency, all locale IDs used in Yii applications should be canonicalized to the format of ll-CC, where ll is a two- or three-letter lowercase language code according to ISO-639 and CC is a two-letter country code according to ISO-3166. More details about locale can be found in check the documentation of the ICU project.

In Yii, we often use the term “language” to refer to a locale.

A Yii application uses two kinds of languages: [[yii\base\Application::$sourceLanguage|source language]] and [[yii\base\Application::$language|target language]]. The former refers to the language in which the text messages in the source code are written, while the latter is the language that should be used to display content to end users. The so-called message translation service mainly translates a text message from source language to target language.

You can configure application languages in the application configuration like the following:

return [
    // set target language to be Russian
    'language' => 'ru-RU',
    // set source language to be English
    'sourceLanguage' => 'en-US',
    ......
];

The default value for the [[yii\base\Application::$sourceLanguage|source language]] is en-US, meaning US English. It is recommended that you keep this default value unchanged, because it is usually much easier to find people who can translate from English to other languages than from non-English to non-English.

You often need to set the [[yii\base\Application::$language|target language]] dynamically based on different factors, such as the language preference of end users. Instead of configuring it in the application configuration, you can use the following statement to change the target language:

// change target language to Chinese
\Yii::$app->language = 'zh-CN';

Message Translation

The message translation service translates a text message from one language (usually the [[yii\base\Application::$sourceLanguage|source language]]) to another (usually the [[yii\base\Application::$language|target language]]). It does the translation by looking up the message to be translated in a message source which stores the original messages and the translated messages. If the message is found, the corresponding translated message will be returned; otherwise the original message will be returned untranslated.

To use the message translation service, you mainly need to do the following work:

• Wrap every text message that needs to be translated in a call to the [[Yii::t()]] method;
• Configure one or multiple message sources in which the message translation service can look for translated messages;
• Let the translators to translate messages and store them in the message source(s).

The method [[Yii::t()]] can be used like the following,

echo \Yii::t('app', 'This is a string to translate!');

where the second parameter refers to the text message to be translated, while the first parameter refers to the name of the category which is used to categorize the message.

The [[Yii::t()]] method will call the i18n application component to perform the actual translation work. The component can be configured in the application configuration as follows,

'components' => [
    // ...
    'i18n' => [
        'translations' => [
            'app*' => [
                'class' => 'yii\i18n\PhpMessageSource',
                //'basePath' => '@app/messages',
                //'sourceLanguage' => 'en-US',
                'fileMap' => [
                    'app' => 'app.php',
                    'app/error' => 'error.php',
                ],
            ],
        ],
    ],
],

In the above code, a message source supported by [[yii\i18n\PhpMessageSource]] is being configured. The pattern app* indicates that all message categories whose names start with app should be translated using this message source. The [[yii\i18n\PhpMessageSource]] class uses PHP files to store message translations. Each PHP file corresponds to the messages of a single category. By default, the file name should be the same as the category name. However, you may configure [[yii\i18n\PhpMessageSource::fileMap|fileMap]] to map a category to a PHP file with a different naming approach. In the above example, the category app/error is mapped to the PHP file @app/messages/ru-RU/error.php (assuming ru-RU is the target language). Without this configuration, the category would be mapped to @app/messages/ru-RU/app/error.php, instead.

Beside storing the messages in PHP files, you may also use the following message sources to store translated messages in different storage:

• [[yii\i18n\GettextMessageSource]] uses GNU Gettext MO or PO files to maintain translated messages.
• [[yii\i18n\DbMessageSource]] uses a database table to store translated messages.

Message Formatting

When translating a message, you can embed some placeholders and have them replaced by dynamic parameter values. You can even use special placeholder syntax to have the parameter values formatted according to the target language. In this subsection, we will describe different ways of formatting messages.

Message Parameters

In a message to be translated, you can embed one or multiple placeholders so that they can be replaced by the given parameter values. By giving different sets of parameter values, you can variate the translated message dynamically. In the following example, the placeholder {username} in the message 'Hello, {username}!' will be replaced by 'Alexander' and 'Qiang', respectively.

$username = 'Alexander';
// display a translated message with username being "Alexander"
echo \Yii::t('app', 'Hello, {username}!', [
    'username' => $username,
]);
$username = 'Qiang';
// display a translated message with username being "Qiang"
echo \Yii::t('app', 'Hello, {username}!', [
    'username' => $username,
]);

While translating a message containing placeholders, you should leave the placeholders as is. This is because the placeholders will be replaced with the actual parameter values when you call Yii::t() to translate a message.

You can use either named placeholders or positional placeholders, but not both, in a single message.

The previous example shows how you can use named placeholders. That is, each placeholder is written in the format of {ParameterName}, and you provide the parameters as an associative array whose keys are the parameter names (without the curly brackets) and whose values are the corresponding parameter values.

Positional placeholders use zero-based integer sequence as placeholders which are replaced by the parameter values according to their positions in the call of Yii::t(). In the following example, the positional placeholders {0}, {1} and {2} will be replaced by the values of $price, $count and $subtotal, respectively.

$price = 100;
$count = 2;
$subtotal = 200;
echo \Yii::t('app', 'Price: {0}, Count: {1}, Subtotal: {2}', $price, $count, $subtotal);

Tip: In most cases you should use named placeholders. This is because the parameter names will make the translators understand better the whole messages being translated.

Parameter Formatting

You can specify additional formatting rules in the placeholders of a message so that the parameter values can be formatted properly before they replace the placeholders. In the following example, the price parameter value will be treated as a number and formatted as a currency value:

$price = 100;
echo \Yii::t('app', 'Price: {0, number, currency}', $price);

Note: Parameter formatting requires the installation of the intl PHP extension.

You can use either the short form or the full form to specify a placeholder with formatting:

short form: {PlaceholderName, ParameterType}
full form: {PlaceholderName, ParameterType, ParameterStyle}

Please refer to the ICU documentation for the complete instructions on how to specify such placeholders.

In the following we will show some common usages.

Number

The parameter value is treated as a number. For example,

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

You can specify an optional parameter style as integer, currency, or percent:

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

You can also specify a custom pattern to format the number. For example,

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

Formatting reference.

Date

The parameter value should be formatted as a date. For example,

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

You can specify an optional parameter style as short, medium, long, or full:

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

You can also specify a custom pattern to format the date value:

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

Formatting reference.

Time

The parameter value should be formatted as a time. For example,

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

You can specify an optional parameter style as short, medium, long, or full:

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

You can also specify a custom pattern to format the time value:

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

Formatting reference.

Spellout

The parameter value should be treated as a number and formatted as a spellout. For example,

// may produce "42 is spelled as forty-two"
echo \Yii::t('app', '{n,number} is spelled as {n, spellout}', ['n' => 42]);

Ordinal

The parameter value should be treated as a number and formatted as an ordinal name. For example,

// may produce "You are the 42nd visitor here!"
echo \Yii::t('app', 'You are the {n, ordinal} visitor here!', ['n' => 42]);

Duration

The parameter value should be treated as the number of seconds and formatted as a time duration string. For example,

// may produce "You are here for 47 sec. already!"
echo \Yii::t('app', 'You are here for {n, duration} already!', ['n' => 47]);

Plural

Different languages have different ways to inflect plurals. Yii provides a convenient way for translating messages in different plural forms that works well even for very complex rules. Instead of dealing with the inflection rules directly, it is sufficient to provide the translation of inflected words in certain situations only. For example,

// When $n = 0, it may produce "There are no cats!"
// When $n = 1, it may produce "There is one cat!"
// When $n = 42, it may produce "There are 42 cats!"
echo \Yii::t('app', 'There {n, plural, =0{are no cats} =1{is one cat} other{are # cats}}!', ['n' => $n]);

In the plural rule arguments above, =0 means exactly zero, =1 means exactly one, and other is for any other value. # is replaced with the value of n.

Plural forms can be very complicated in some languages. In the following Russian example, =1 matches exactly n = 1 while one matches 21 or 101:

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

Note that the above message is mainly used as a translated message, not an original message, unless you set the [[yii\base\Application::$sourceLanguage|source language]] of your application as ru-RU.

When a translation is not found for an original message, the plural rules for the [[yii\base\Application::$sourceLanguage|source language]] will be applied to the original message.

To learn which inflection forms you should specify for a particular language, please refer to the rules reference at unicode.org.

Selection

You can use the select parameter type to choose a phrase based on the parameter value. For example,

// It may produce "Snoopy is a dog and it loves Yii!"
echo \Yii::t('app', '{name} is a {gender} and {gender, select, female{she} male{he} other{it}} loves Yii!', [
    'name' => 'Snoopy',
    'gender' => 'dog',
]);

In the expression above, both female and male are possible parameter values, while other handles values that do not match either one of them. Following each possible parameter value, you should specify a phrase and enclose it in a pair of curly brackets.

Specifying default translation

You can specify default translations that will be used as a fallback for categories that don’t match any other translation. This translation should be marked with *. In order to do it add the following to the application config:

//configure i18n component
'i18n' => [
    'translations' => [
        '*' => [
            'class' => 'yii\i18n\PhpMessageSource'
        ],
    ],
],

Now you can use categories without configuring each one, which is similar to Yii 1.1 behavior. Messages for the category will be loaded from a file under the default translation basePath that is @app/messages:

echo Yii::t('not_specified_category', 'message from unspecified category');

The message will be loaded from @app/messages/<LanguageCode>/not_specified_category.php.

Translating module messages

If you want to translate the messages for a module and avoid using a single translation file for all the messages, you can do it like the following:

<?php
namespace app\modules\users;
use Yii;
class Module extends \yii\base\Module
{
    public $controllerNamespace = 'app\modules\users\controllers';
    public function init()
    {
        parent::init();
        $this->registerTranslations();
    }
    public function registerTranslations()
    {
        Yii::$app->i18n->translations['modules/users/*'] = [
            'class' => 'yii\i18n\PhpMessageSource',
            'sourceLanguage' => 'en-US',
            'basePath' => '@app/modules/users/messages',
            'fileMap' => [
                'modules/users/validation' => 'validation.php',
                'modules/users/form' => 'form.php',
                ...
            ],
        ];
    }
    public static function t($category, $message, $params = [], $language = null)
    {
        return Yii::t('modules/users/' . $category, $message, $params, $language);
    }
}

In the example above we are using wildcard for matching and then filtering each category per needed file. Instead of using fileMap, you can simply use the convention of the category mapping to the same named file. Now you can use Module::t('validation', 'your custom validation message') or Module::t('form', 'some form label') directly.

Translating widgets messages

The same rule as applied for Modules above can be applied for widgets too, for example:

<?php
namespace app\widgets\menu;
use yii\base\Widget;
use Yii;
class Menu extends Widget
{
    public function init()
    {
        parent::init();
        $this->registerTranslations();
    }
    public function registerTranslations()
    {
        $i18n = Yii::$app->i18n;
        $i18n->translations['widgets/menu/*'] = [
            'class' => 'yii\i18n\PhpMessageSource',
            'sourceLanguage' => 'en-US',
            'basePath' => '@app/widgets/menu/messages',
            'fileMap' => [
                'widgets/menu/messages' => 'messages.php',
            ],
        ];
    }
    public function run()
    {
        echo $this->render('index');
    }
    public static function t($category, $message, $params = [], $language = null)
    {
        return Yii::t('widgets/menu/' . $category, $message, $params, $language);
    }
}

Instead of using fileMap you can simply use the convention of the category mapping to the same named file. Now you can use Menu::t('messages', 'new messages {messages}', ['{messages}' => 10]) directly.

Note: For widgets you also can use i18n views, with the same rules as for controllers being applied to them too.

Translating framework messages

Yii comes with the default translation messages for validation errors and some other strings. These messages are all in the category yii. Sometimes you want to correct the default framework message translation for your application. In order to do so, configure the i18n application component like the following:

'i18n' => [
    'translations' => [
        'yii' => [
            'class' => 'yii\i18n\PhpMessageSource',
            'sourceLanguage' => 'en-US',
            'basePath' => '@app/messages'
        ],
    ],
],

Now you can place your adjusted translations to @app/messages/<language>/yii.php.

Handling missing translations

Even if the translation is missing from the source, Yii will display the requested message content. Such behavior is very convenient in case your raw message is a valid verbose text. However, sometimes it is not enough. You may need to perform some custom processing of the situation, when the requested translation is missing from the source. This can be achieved using the [[yii\i18n\MessageSource::EVENT_MISSING_TRANSLATION|missingTranslation]]-event of [[yii\i18n\MessageSource]].

For example, you may want to mark all the missing translations with something notable, so that they can be easily found at the page. First you need to setup an event handler. This can be done in the application configuration:

'components' => [
    // ...
    'i18n' => [
        'translations' => [
            'app*' => [
                'class' => 'yii\i18n\PhpMessageSource',
                'fileMap' => [
                    'app' => 'app.php',
                    'app/error' => 'error.php',
                ],
                'on missingTranslation' => ['app\components\TranslationEventHandler', 'handleMissingTranslation']
            ],
        ],
    ],
],

Now you need to implement your own event handler:

<?php
namespace app\components;
use yii\i18n\MissingTranslationEvent;
class TranslationEventHandler
{
    public static function handleMissingTranslation(MissingTranslationEvent $event)
    {
        $event->translatedMessage = "@MISSING: {$event->category}.{$event->message} FOR LANGUAGE {$event->language} @";
    }
}

If [[yii\i18n\MissingTranslationEvent::translatedMessage]] is set by the event handler it will be displayed as the translation result.

Note: each message source handles its missing translations separately. If you are using several message sources and wish them to treat the missing translations in the same way, you should assign the corresponding event handler to each of them.

Using the message command

Translations can be stored in [[yii\i18n\PhpMessageSource|php files]], [[yii\i18n\GettextMessageSource|.po files] or to [[yii\i18n\DbMessageSource|database]]. See specific classes for additional options.

First of all you need to create a config file. Decide where you want to store it and then issue the command

./yii message/config path/to/config.php

Open the created file and adjust the parameters to fit your needs. Pay special attention to:

• languages: an array representing what languages your app should be translated to;
• messagePath: path where to store message files, which should match the i18n‘s basePath parameter stated in config.

Note that aliases are not supported here, they must be real path relative to the config file location

Once you’re done with the config file you can finally extract your messages with the command

./yii message path/to/config.php

You will then find your files (if you’ve chosen file based translations) in your messagePath directory.

View Translation

Instead of translating individual text messages, sometimes you may want to translate a whole view script. To achieve this goal, simply translate the view and save it under a subdirectory whose name is the same as target language. For example, if you want to translate the view script views/site/index.php and the target language is ru-RU, you may translate the view and save it as the file views/site/ru-RU/index.php. Now whenever you call [[yii\base\View::renderFile()]] or any method that invoke this method (e.g. [[yii\base\Controller::render()]]) to render the view views/site/index.php, it will end up rendering the translated view views/site/ru-RU/index.php, instead.

Note: If the [[yii\base\Application::$language|target language]] is the same as [[yii\base\Application::$sourceLanguage|source language]], view translation may still work as long as you provide a translated view. For example, if both languages are en-US and you have both views/site/index.php and views/site/en-US/index.php, then the latter will be rendered.

Formatting Date and Number Values

See the Data Formatting section for details.

Setting Up PHP Environment

Yii uses the PHP intl extension to provide most of its I18N features, such as the date and number formatting of the [[yii\i18n\Formatter]] class and the message formatting using [[yii\i18n\MessageFormatter]]. Both classes provide a fallback mechanism when the intl extension is not installed. However, the fallback implementation only works well for English target language. So it is highly recommended that you install intl when I18N is needed.

The PHP intl extension is based on the ICU library which provides the knowledge and formatting rules for all different locales. Different versions of ICU may produce different formatting result of date and number values. To ensure your website produces the same results across all environments, it is recommended that you install the same version of the intl extension (and thus the same version of ICU) in all environments.

To find out which version of ICU is used by PHP, you can run the following script, which will give you the PHP and ICU version being used.

<?php
echo "PHP: " . PHP_VERSION . "\n";
echo "ICU: " . INTL_ICU_VERSION . "\n";

It is also recommended that you use an ICU version equal or greater than version 49. This will ensure you can use all the features described in this document. For example, an ICU version below 49 does not support using # placeholders in plural rules. Please refer to http://site.icu-project.org/download for a complete list of available ICU versions. Note that the version numbering has changed after the 4.8 release (e.g., ICU 4.8, ICU 49, ICU 50, etc.)

Additionally the information in the time zone database shipped with the ICU library may be outdated. Please refer to the ICU manual for details on updating the time zone database. While for output formatting the ICU timezone database is used, the time zone database used by PHP may be relevant too. You can update it by installing the latest version of the pecl package timezonedb.