yii\filters\ContentNegotiator::negotiateLanguage PHP Метод

    protected function negotiateLanguage($request)
    {
        if (!empty($this->languageParam) && ($language = $request->get($this->languageParam)) !== null) {
            if (isset($this->languages[$language])) {
                return $this->languages[$language];
            }
            foreach ($this->languages as $key => $supported) {
                if (is_int($key) && $this->isLanguageSupported($language, $supported)) {
                    return $supported;
                }
            }
            return reset($this->languages);
        }
        foreach ($request->getAcceptableLanguages() as $language) {
            if (isset($this->languages[$language])) {
                return $this->languages[$language];
            }
            foreach ($this->languages as $key => $supported) {
                if (is_int($key) && $this->isLanguageSupported($language, $supported)) {
                    return $supported;
                }
            }
        }
        return reset($this->languages);
    }