Flarum\Locale\LocaleManager::getJsFiles PHP Method

    public function getJsFiles($locale)
    {
        $files = array_get($this->js, $locale, []);
        $parts = explode('-', $locale);
        if (count($parts) > 1) {
            $files = array_merge(array_get($this->js, $parts[0], []), $files);
        }
        return $files;
    }

 /**
  * Set up the locale compiler for the given locale.
  *
  * @param string $locale
  * @return LocaleJsCompiler
  */
 protected function getLocaleCompiler($locale)
 {
     $compiler = new LocaleJsCompiler($this->getAssetDirectory(), "{$this->clientName}-{$locale}.js");
     foreach ($this->locales->getJsFiles($locale) as $file) {
         $compiler->addFile($file);
     }
     return $compiler;
 }