code: func NewLanguageCompositeFs(base afero.Fs, overlay *LanguageFs) afero.Fs {
  	return afero.NewReadOnlyFs(&languageCompositeFs{afero.NewCopyOnWriteFs(base, overlay).(*afero.CopyOnWriteFs)})
  }
docs: // NewLanguageCompositeFs creates a composite and language aware filesystem.
  // This is a hybrid filesystem. To get a specific file in Open, Stat etc., use the full filename
  // to the target filesystem. This information is available in Readdir, Stat etc. via the
  // special LanguageFileInfo FileInfo implementation.