yii2 i18n学习

举例说明常见的翻译：Yii::t('app','Login')；
追踪源码：BaseYii.php 文件 ，Yii::t($category, $message, $params = [], $language = null) 这个方法实际上是 yiii18nI18N::translate()的一个捷径方法

 /**
     * Translates a message to the specified language.
     *
     * This is a shortcut method of [[yiii18nI18N::translate()]].
     *
     * The translation will be conducted according to the message category and the target language will be used.
     *
     * You can add parameters to a translation message that will be substituted（取代） with the corresponding（相应的） value after
     * translation. The format for this is to use curly brackets around the parameter name as you can see in the following example:
     *
     * ```php
     * $username = 'Alexander';
     * echo Yii::t('app', 'Hello, {username}!', ['username' => $username]);
     * ```
     *
     * Further formatting of message parameters is supported using the [PHP intl extensions](http://www.php.net/manual/en/intro.intl.php)
     * message formatter. See [[yiii18nI18N::translate()]] for more details.
     *
     * @param string $category the message category.
     * @param string $message the message to be translated.
     * @param array $params the parameters that will be used to replace the corresponding placeholders in the message.
     * @param string $language the language code (e.g. `en-US`, `en`). If this is null, the current
     * [[yiiaseApplication::language|application language]] will be used.
     * @return string the translated message.
     */
    public static function t($category, $message, $params = [], $language = null)
    {
        if (static::$app !== null) {
            return static::$app->getI18n()->translate($category, $message, $params, $language ?: static::$app->language);
        } else {
            $p = [];
            foreach ((array) $params as $name => $value) {
                $p['{' . $name . '}'] = $value;
            }

            return ($p === []) ? $message : strtr($message, $p);
        }
    }

查看 yiii18nI18N::translate()方法：

/**
     * Translates a message to the specified language.
     *
     * After translation the message will be formatted using [[MessageFormatter]] if it contains
     * ICU message format and `$params` are not empty.
     *
     * @param string $category the message category.
     * @param string $message the message to be translated.
     * @param array $params the parameters that will be used to replace the corresponding placeholders in the message.
     * @param string $language the language code (e.g. `en-US`, `en`).
     * @return string the translated and formatted message.
     */
    public function translate($category, $message, $params, $language)
    {
        // 返回MessageSource the message source for the given category.
        $messageSource = $this->getMessageSource($category);
        //返回翻译的内容
        $translation = $messageSource->translate($category, $message, $language);
        //格式话翻译的内容
        if ($translation === false) {
            return $this->format($message, $params, $messageSource->sourceLanguage);
        } else {
            return $this->format($translation, $params, $language);
        }
    }

其中 $messageSource = $this->getMessageSource($category);//根据配置文件内容和 给的参数$category 返回继承MessageSource 相应子类的实例对象， 本例根据配置文件返回PhpMessageSource对象

<?php
return [
    'vendorPath' => dirname(dirname(__DIR__)) . '/vendor',
    'components' => [
        'cache' => [
            'class' => 'yiicachingFileCache',
        ],
        'i18n'=>[
            'translations' => [
                'app*'=> [
                    'class' => 'yiii18nPhpMessageSource',
                    'basePath'=>'@common/messages',
                    'fileMap'=>[
                        'app'=>'app.php',
                    ],
                ],
            ],
        ],
    ],
];

 $messageSource = $this->getMessageSource($category); 返回继承MessageSource 相应子类的实例对象

 /**
     * Returns the message source for the given category.
     * @param string $category the category name.
     * @return MessageSource the message source for the given category.
     * @throws InvalidConfigException if there is no message source available for the specified category.
     */
    //根据配置文件内容和 给的参数$category 返回继承MessageSource 相应子类的实例对象， 本例根据配置文件返回PhpMessageSource对象
    public function getMessageSource($category)
    {
        if (isset($this->translations[$category])) {
            $source = $this->translations[$category];
            if ($source instanceof MessageSource) {
                return $source;
            } else {
                return $this->translations[$category] = Yii::createObject($source);
            }
        } else {
            // try wildcard matching
            foreach ($this->translations as $pattern => $source) {
                if (strpos($pattern, '*') > 0 && strpos($category, rtrim($pattern, '*')) === 0) {
                    if ($source instanceof MessageSource) {
                        return $source;
                    } else {
                        return $this->translations[$category] = $this->translations[$pattern] = Yii::createObject($source);
                    }
                }
            }
            // match '*' in the last
            if (isset($this->translations['*'])) {
                $source = $this->translations['*'];
                if ($source instanceof MessageSource) {
                    return $source;
                } else {
                    return $this->translations[$category] = $this->translations['*'] = Yii::createObject($source);
                }
            }
        }

        throw new InvalidConfigException("Unable to locate message source for category '$category'.");
    }

再根据实例对象的translate方法返回翻译的内容，  $translation = $messageSource->translate($category, $message, $language);

 MessageSource  类的 translate方法如下：

  /**
     * Translates a message to the specified language.
     *
     * Note that unless [[forceTranslation]] is true, if the target language
     * is the same as the [[sourceLanguage|source language]], the message
     * will NOT be translated.
     *
     * If a translation is not found, a [[EVENT_MISSING_TRANSLATION|missingTranslation]] event will be triggered.
     *
     * @param string $category the message category
     * @param string $message the message to be translated
     * @param string $language the target language
     * @return string|boolean the translated message or false if translation wasn't found or isn't required
     */
    // 翻译一段信息为指定的语言文件下的内容
    public function translate($category, $message, $language)
    {
        if ($this->forceTranslation || $language !== $this->sourceLanguage) {
           
            return $this->translateMessage($category, $message, $language);
        } else {
            return false;
        }
    }

$this->translateMessage($category, $message, $language);

 /**
     * Translates the specified message.
     * If the message is not found, a [[EVENT_MISSING_TRANSLATION|missingTranslation]] event will be triggered.
     * If there is an event handler, it may provide a [[MissingTranslationEvent::$translatedMessage|fallback translation]].
     * If no fallback translation is provided this method will return `false`.
     * @param string $category the category that the message belongs to.
     * @param string $message the message to be translated.
     * @param string $language the target language.
     * @return string|boolean the translated message or false if translation wasn't found.
     */
    protected function translateMessage($category, $message, $language)
    {
        $key = $language . '/' . $category;
        if (!isset($this->_messages[$key])) {
            // $language = 'zh-CN'  $category = 'app'
            // $this->loadMessages($category, $language) 为合并后的指定类别语言的翻译数组 key => value
            $this->_messages[$key] = $this->loadMessages($category, $language);
        }
        if (isset($this->_messages[$key][$message]) && $this->_messages[$key][$message] !== '') {
            return $this->_messages[$key][$message];
        } elseif ($this->hasEventHandlers(self::EVENT_MISSING_TRANSLATION)) {
            $event = new MissingTranslationEvent([
                'category' => $category,
                'message' => $message,
                'language' => $language,
            ]);
            $this->trigger(self::EVENT_MISSING_TRANSLATION, $event);
            if ($event->translatedMessage !== null) {
                return $this->_messages[$key][$message] = $event->translatedMessage;
            }
        }

        return $this->_messages[$key][$message] = false;
    }

根据配置文件生成的 MessageSource子类相应对象的loadMessages方法，生成翻译的文件数组内容，在根据内容查找相应的以$message为键的对应值：
return $this->_messages[$key][$message];

本例根据PhpMessageSource对象的translateMessage方法为例说明：

  /**
     * Loads the message translation for the specified $language and $category.
     * If translation for specific locale code such as `en-US` isn't found it
     * tries more generic `en`. When both are present, the `en-US` messages will be merged
     * over `en`. See [[loadFallbackMessages]] for details.
     * If the $language is less specific than [[sourceLanguage]], the method will try to
     * load the messages for [[sourceLanguage]]. For example: [[sourceLanguage]] is `en-GB`,
     * $language is `en`. The method will load the messages for `en` and merge them over `en-GB`.
     *
     * @param string $category the message category
     * @param string $language the target language
     * @return array the loaded messages. The keys are original messages, and the values are the translated messages.
     * @see loadFallbackMessages
     * @see sourceLanguage
     */
    protected function loadMessages($category, $language)
    {
        //返回指定类别和语言的文件路径
        $messageFile = $this->getMessageFilePath($category, $language);
        // 根据文件路径，加载翻译文件，为数组键值对
        $messages = $this->loadMessagesFromFile($messageFile);

        $fallbackLanguage = substr($language, 0, 2);
        $fallbackSourceLanguage = substr($this->sourceLanguage, 0, 2);

        if ($language !== $fallbackLanguage) {
            // $language = 'zh-CN'    $fallbackLanguage = 'zh'  合并语言zh-CN和zh文件为新的$messages
            $messages = $this->loadFallbackMessages($category, $fallbackLanguage, $messages, $messageFile);
        } elseif ($language === $fallbackSourceLanguage) {
            //  $language = 'zh'    $fallbackLanguage = 'zh' $this->sourceLanguage = 'en' 合并zh 文件和en 文件，当zh文件翻译key的value信息没有时用 en 文件的相应的value 替代，合并为新的翻译数组内容 $messages
            $messages = $this->loadFallbackMessages($category, $this->sourceLanguage, $messages, $messageFile);
        } else {
            if ($messages === null) {
                Yii::error("The message file for category '$category' does not exist: $messageFile", __METHOD__);
            }
        }

        return (array) $messages;
    }

 //返回指定类别和语言的文件路径
$messageFile = $this->getMessageFilePath($category, $language);

 /**
     * Returns message file path for the specified language and category.
     *
     * @param string $category the message category
     * @param string $language the target language
     * @return string path to message file
     */
    //返回指定的语言和类别文件路径
    protected function getMessageFilePath($category, $language)
    {
        //语言类别文件路径
        $messageFile = Yii::getAlias($this->basePath) . "/$language/";
        if (isset($this->fileMap[$category])) {
            $messageFile .= $this->fileMap[$category];
        } else {
            $messageFile .= str_replace('\', '/', $category) . '.php';
        }

        return $messageFile;
    }

// 根据文件路径，加载翻译文件，为数组键值对
$messages = $this->loadMessagesFromFile($messageFile);

 /**
     * Loads the message translation for the specified language and category or returns null if file doesn't exist.
     *
     * @param string $messageFile path to message file
     * @return array|null array of messages or null if file not found
     */
    //加载翻译文件，翻译文件为数组文件
    protected function loadMessagesFromFile($messageFile)
    {
        if (is_file($messageFile)) {
            $messages = include($messageFile);
            if (!is_array($messages)) {
                $messages = [];
            }

            return $messages;
        } else {
            return null;
        }
    }

//根据不同的条件,从其他文件中补充语言文件的缺少的key 的值value 
$messages = $this->loadFallbackMessages($category, $this->sourceLanguage, $messages, $messageFile);

/**
     * The method is normally called by [[loadMessages]] to load the fallback messages for the language.
     * Method tries to load the $category messages for the $fallbackLanguage and adds them to the $messages array.
     *
     * @param string $category the message category
     * @param string $fallbackLanguage the target fallback language
     * @param array $messages the array of previously loaded translation messages.
     * The keys are original messages, and the values are the translated messages.
     * @param string $originalMessageFile the path to the file with messages. Used to log an error message
     * in case when no translations were found.
     * @return array the loaded messages. The keys are original messages, and the values are the translated messages.
     * @since 2.0.7
     */
    protected function loadFallbackMessages($category, $fallbackLanguage, $messages, $originalMessageFile)
    {
        // 返回的信息文件路径
        $fallbackMessageFile = $this->getMessageFilePath($category, $fallbackLanguage);
        //根据文件路径信息，加载文件的内容
        $fallbackMessages = $this->loadMessagesFromFile($fallbackMessageFile);

        if (
            $messages === null && $fallbackMessages === null
            && $fallbackLanguage !== $this->sourceLanguage
            && $fallbackLanguage !== substr($this->sourceLanguage, 0, 2)
        ) {
            Yii::error("The message file for category '$category' does not exist: $originalMessageFile "
                . "Fallback file does not exist as well: $fallbackMessageFile", __METHOD__);
        } elseif (empty($messages)) {
            return $fallbackMessages;
        } elseif (!empty($fallbackMessages)) {
            // 当$message数组key 值为空时，且$fallbackMessages对应的key的翻译内容存在是，把$fallbackMessages的内容翻译数组赋值给 $messages[$key]
            foreach ($fallbackMessages as $key => $value) {
                if (!empty($value) && empty($messages[$key])) {
                    $messages[$key] = $fallbackMessages[$key];
                }
            }
        }

        return (array) $messages;
    }

最后返回$messages:

return (array) $messages;

根据提供的参数（$message）把$message作为key 查找 $messages 数组中对应的key的值