code: func NewLanguageFs(lang string, languages map[string]bool, fs afero.Fs) *LanguageFs {
  	if lang == "" {
  		panic("no lang set for the language fs")
  	}
  	var basePath string
  
  	if bfs, ok := fs.(*afero.BasePathFs); ok {
  		basePath, _ = bfs.RealPath("")
  	}
  
  	marker := hugoFsMarker + "_" + lang + "_"
  
  	return &LanguageFs{lang: lang, languages: languages, basePath: basePath, Fs: fs, nameMarker: marker}
  }
docs: // NewLanguageFs creates a new language filesystem.