code: public function getFallbackLocale()
      {
          if ($this->overrideFallbackLocale) {
              return $this->overrideFallbackLocale;
          }
  
          if (property_exists($this, 'fallbackLocale')) {
              return $this->fallbackLocale;
          }
  
          return TranslatableConfig::fallbackLocale();
      }
docs: Get current locale
  
  @return string