framework/i18n/DbMessageSource.php
protected function loadMessages($category, $language)
    {
        if ($this->enableCaching) {
            $key = [
                __CLASS__,
                $category,
                $language,
            ];
            $messages = $this->cache->get($key);
            if ($messages === false) {
                $messages = $this->loadMessagesFromDb($category, $language);
                $this->cache->set($key, $messages, $this->cachingDuration);
            }

            return $messages;
        }

        return $this->loadMessagesFromDb($category, $language);
    }
protected function loadMessages($category, $language)
    {
        if ($this->enableCaching) {
            $key = [
                __CLASS__,
                $category,
                $language,
            ];
            $messages = $this->cache->get($key);
            if ($messages === false) {
                $messages = $this->loadMessagesFromDb($category, $language);
                $this->cache->set($key, $messages, $this->cachingDuration);
            }

            return $messages;
        }

        return $this->loadMessagesFromDb($category, $language);
    }
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`.

@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 translated messages.