Piwik\Plugins\LanguagesManager\LanguagesManager::initLanguage PHP Method

    public function initLanguage()
    {
        /** @var Translator $translator */
        $translator = StaticContainer::get('Piwik\\Translation\\Translator');
        $language = Common::getRequestVar('language', '', 'string');
        if (empty($language)) {
            $userLanguage = self::getLanguageCodeForCurrentUser();
            if (API::getInstance()->isLanguageAvailable($userLanguage)) {
                $language = $userLanguage;
            }
        }
        if (!empty($language) && API::getInstance()->isLanguageAvailable($language)) {
            $translator->setCurrentLanguage($language);
        }
        $locale = $translator->translate('General_Locale');
        Locale::setLocale($locale);
    }