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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 provides support for I18N in several aspects.

  • It provides the locale data for each possible language and variant.
  • It provides message and file translation service.
  • It provides locale-dependent date and time formatting.
  • It provides locale-dependent number formatting.

In the following subsections, we will elaborate each of the above aspects.

1. 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 in Yii are canonicalized to the format of LanguageID or LanguageID_RegionID in lower case (e.g. en, en_us).

Locale data is represented as a CLocale instance. It provides locale-dependent information, including currency symbols, number symbols, currency formats, number formats, date and time formats, and date-related names. Since the language information is already implied in the locale ID, it is not provided by CLocale. For the same reason, we often interchangeably use the term locale and language.

Given a locale ID, one can get the corresponding CLocale instance by CLocale::getInstance($localeID) or CApplication::getLocale($localeID).

Info: Yii comes with locale data for nearly every language and region. The data is obtained from Common Locale Data Repository (CLDR). For each locale, only a subset of the CLDR data is provided as the original data contains a lot of rarely used information. Users can also supply their own customized locale data. To do so, configure the CApplication::localeDataPath property with the directory that contains the customized locale data. Please refer to the locale data files under framework/i18n/data in order to create customized locale data files.

For a Yii application, we differentiate its target language from source language. The target language is the language (locale) of the users that the application is targeted at, while the source language refers to the language (locale) that the application source files are written in. Internationalization occurs only when the two languages are different.

Tip: It's better to leave English as a source language since it will be easier to find people translating from English to any other language.

One can configure target language in the application configuration, or change it dynamically before any internationalization occurs.

Tip: Sometimes, we may want to set the target language as the language preferred by a user (specified in the user's browser preferences). To do so, we can retrieve the user preferred language ID using CHttpRequest::preferredLanguage.

2. Translation

The most needed I18N feature is perhaps translation, including message translation and view translation. The former translates a text message to the desired language, while the latter translates a whole file to the desired language.

A translation request consists of the object to be translated, the source language that the object is in, and the target language that the object needs to be translated to. In Yii, the source language defaults to the application source language while the target language defaults to the application language. If the source and target languages are the same, translation will not occur.

Message Translation

Message translation is done by calling Yii::t(). The method translates the given message from source language to target language.

When translating a message, its category has to be specified since a message may be translated differently under different categories (contexts). The category yii is reserved for messages used by the Yii framework core code.

Messages can contain parameter placeholders which will be replaced with the actual parameter values when calling Yii::t(). For example, the following message translation request would replace the {alias} placeholder in the original message with the actual alias value.

Yii::t('app', 'Path alias "{alias}" is redefined.',

Note: Messages to be translated must be constant strings. They should not contain variables that would change message content (e.g. "Invalid {$message} content."). Use parameter placeholders if a message needs to vary according to some parameters.

Translated messages are stored in a repository called message source. A message source is represented as an instance of CMessageSource or its child class. When Yii::t() is invoked, it will look for the message in the message source and return its translated version if it is found.

Yii comes with the following types of message sources. You may also extend CMessageSource to create your own message source type.

  • CPhpMessageSource: the message translations are stored as key-value pairs in a PHP array. The original message is the key and the translated message is the value. Each array represents the translations for a particular category of messages and is stored in a separate PHP script file whose name is the category name. The PHP translation files for the same language are stored under the same directory named as the locale ID. And all these directories are located under the directory specified by basePath.

  • CGettextMessageSource: the message translations are stored as GNU Gettext files.

  • CDbMessageSource: the message translations are stored in database tables. For more details, see the API documentation for CDbMessageSource.

A message source is loaded as an application component. Yii pre-declares an application component named messages to store messages that are used in user application. By default, the type of this message source is CPhpMessageSource and the base path for storing the PHP translation files is protected/messages.

In summary, in order to use message translation, the following steps are needed:

  1. Call Yii::t() at appropriate places;

  2. Create PHP translation files as protected/messages/LocaleID/CategoryName.php. Each file simply returns an array of message translations. Note, this assumes you are using the default CPhpMessageSource to store the translated messages.

  3. Configure CApplication::sourceLanguage and CApplication::language.

Tip: The yiic tool in Yii can be used to manage message translations when CPhpMessageSource is used as the message source. Its message command can automatically extract messages to be translated from selected source files and merge them with existing translations if necessary. For more details of using the message command, please run yiic help message.

When using CPhpMessageSource to manage message source, messages for an extension class (e.g. a widget, a module) can be specially managed and used. In particular, if a message belongs to an extension whose class name is Xyz, then the message category can be specified in the format of Xyz.categoryName. The corresponding message file will be assumed to be BasePath/messages/LanguageID/categoryName.php, where BasePath refers to the directory that contains the extension class file. And when using Yii::t() to translate an extension message, the following format should be used, instead:

Yii::t('Xyz.categoryName', 'message to be translated')

Yii supports choice format, which is also known as plural forms. Choice format refers to choosing a translation according to a given number value. For example, in English, the word 'book' may either take a singular form or a plural form depending on the number of books, while in other languages, the word may not use different forms (such as in Chinese) or may use more complex plural form rules (such as in Russian). Choice format solves this problem in a simple yet effective way.

To use choice format, a translated message must consist of a sequence of expression-message pairs separated by |, as shown below:


where exprN refers to a valid PHP expression which evaluates to a boolean value indicating whether the corresponding message should be returned. Only the message corresponding to the first expression that evaluates to true will be returned. An expression can contain a special variable named n (note, it is not $n) which will take the number value passed as the first message parameter. For example, assuming a translated message is:

'n==1#one book|n>1#many books'

and we are passing a number value 2 in the message parameter array when calling Yii::t(), we would obtain many books as the final translated message:

Yii::t('app', 'n==1#one book|n>1#many books', array(1));
//or since 1.1.6
Yii::t('app', 'n==1#one book|n>1#many books', 1);

As a shortcut notation, if an expression is a number, it will be treated as n==Number. Therefore, the above translated message can be also be written as:

'1#one book|n>1#many books'

Plural forms format

Since version 1.1.6 CLDR-based plural choice format can be used with a simpler syntax. It is handy for languages with complex plural form rules.

The rule for English plural forms above can be written in the following way:

Yii::t('test', 'cucumber|cucumbers', 1);
Yii::t('test', 'cucumber|cucumbers', 2);
Yii::t('test', 'cucumber|cucumbers', 0);

The code above will give you:


If you want to include number you can use the following code.

echo Yii::t('test', '{n} cucumber|{n} cucumbers', 1);

Here {n} is a special placeholder holding number passed. It will print 1 cucumber.

You can pass additional parameters:

Yii::t('test', '{username} has a cucumber|{username} has {n} cucumbers',
array(5, '{username}' => 'samdark'));

and even replace a number parameter with something else:

function convertNumber($number)
    // convert number to word
    return $number;
Yii::t('test', '{n} cucumber|{n} cucumbers',
array(5, '{n}' => convertNumber(5)));

The number of plural expressions will vary by language. For example:

Yii::t('app', '{n} cucumber|{n} cucumbers', 62);
Yii::t('app', '{n} cucumber|{n} cucumbers', 1.5);
Yii::t('app', '{n} cucumber|{n} cucumbers', 1);
Yii::t('app', '{n} cucumber|{n} cucumbers', 7);

when translated into Russian will have 4 instead of 2 message expressions:

'{n} cucumber|{n} cucumbers' => '{n} огурец|{n} огурца|{n} огурцов|{n} огурца',

which will produce:

62 огурца
1.5 огурца
1 огурец
7 огурцов

Info: to learn about how many expressions you should supply and in which order they should be, please refer to CLDR Language Plural Rules page.

File Translation

File translation is accomplished by calling CApplication::findLocalizedFile(). Given the path of a file to be translated, the method will look for a file with the same name under the LocaleID subdirectory. If found, the file path will be returned; otherwise, the original file path will be returned.

File translation is mainly used when rendering a view. When calling one of the render methods in a controller or widget, the view files will be translated automatically. For example, if the target language is zh_cn while the source language is en_us, rendering a view named edit would resulting in searching for the view file protected/views/ControllerID/zh_cn/edit.php. If the file is found, this translated version will be used for rendering; otherwise, the file protected/views/ControllerID/edit.php will be rendered instead.

File translation may also be used for other purposes, for example, to display a translated image or load a locale-dependent data file.

3. Date and Time Formatting

Date and time are often in different formats in different countries or regions. The task of date and time formatting is thus to generate a date or time string that fits the specified locale. Yii provides CDateFormatter for this purpose.

Each CDateFormatter instance is associated with a target locale. To get the formatter associated with the target locale of the whole application, we can simply access the dateFormatter property of the application.

The CDateFormatter class mainly provides two methods to format a UNIX timestamp.

  • format: this method formats the given UNIX timestamp into a string according to a customized date-time pattern (e.g. $dateFormatter->format('yyyy-MM-dd',$timestamp)).

  • formatDateTime: this method formats the given UNIX timestamp into a string according to a pattern predefined in the target locale data (e.g. short format of date, long format of time).

4. Number Formatting

Like data and time, numbers may also need to be formatted differently in different countries or regions. Number formatting includes decimal formatting, currency formatting and percentage formatting. Yii provides CNumberFormatter for these tasks.

To get the number formatter associated with the target locale of the whole application, we can access the numberFormatter property of the application.

The following methods are provided by CNumberFormatter to format an integer or double value.

  • format: this method formats the given number into a string according to a customized pattern (e.g. $numberFormatter->format('#,##0.00',$number)).

  • formatDecimal: this method formats the given number using the decimal pattern predefined in the target locale data.

  • formatCurrency: this method formats the given number and currency code using the currency pattern predefined in the target locale data.

  • formatPercentage: this method formats the given number using the percentage pattern predefined in the target locale data.

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