src/ChrisKonnertz/DeepLy/DeepLy.php
public function supportsLangCode($langCode, $allowAuto = false)
    {
        if (! is_string($langCode)) {
            throw new \InvalidArgumentException('The $langCode argument has to be a string');
        }

        $supported = in_array($langCode, $this->getLangCodes($allowAuto));

        return $supported;
    }
public function supportsLangCode($langCode, $allowAuto = false)
    {
        if (! is_string($langCode)) {
            throw new \InvalidArgumentException('The $langCode argument has to be a string');
        }

        $supported = in_array($langCode, $this->getLangCodes($allowAuto));

        return $supported;
    }
Decides if a language (code) is supported by DeepL(y).
Note that 'auto' is not a valid value in this context
except you explicitly set the $allowAuto param to true

@param string $langCode  The language code, for example 'EN'
@param bool   $allowAuto Optional: If false, 'auto' is not a valid language
@return bool