framework/filters/ContentNegotiator.php
protected function negotiateLanguage($request)
    {
        if (!empty($this->languageParam) && ($language = $request->get($this->languageParam)) !== null) {
            if (is_array($language)) {
                // If an array received, then skip it and use the first of supported languages
                return reset($this->languages);
            }
            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($this->languages);
    }
protected function negotiateLanguage($request)
    {
        if (!empty($this->languageParam) && ($language = $request->get($this->languageParam)) !== null) {
            if (is_array($language)) {
                // If an array received, then skip it and use the first of supported languages
                return reset($this->languages);
            }
            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);
    }
Negotiates the application language.
@param Request $request
@return string the chosen language