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Swift 3: NSAttributedString – localization/translation

  • 11.01.2018

If you want to translate an attributed string with XCode, it is not easy.
Normal strings can be translated with NSLocalizedString(key: comment).

However, there is a problem with attributed strings. The attributes must be placed in the correct place in the string and this can vary greatly depending on the language.

One approach I found and which inspired me to my solution was the creation of an RTF (Rich Text Format) file.
The text/string has been designed and localized (in the utility area).

With the function NSAttributedString.init(url: options: documentAttributes) I tried to load the contents of the RTF file. Unfortunately I was not able to load the content, although the RTF file was inside the bundle.

Next I found out that it works with HTML files, too. In principle, I used the same scheme as with RTF files. And this time it worked.

However, I find it difficult to create a separate HTML file for each translation and since HTML is a markup language in contrast to RTF, the consequence was that I tried to extend the normal language files with HTML content and to gain the attributed string from it.

Here is an example:

"Hello %1$@, by registering you accept our <u>Terms of use&gt; </u>.".;

For the translation I use a string extension myself:

extension String {
  var localized: String {
    return NSLocalizedString(self, comment: "")

This can be used like this: “BUTTON_TERMS_OF_USE”.localized.
If you also have placeholders in the text, you can do this again with
of a string extension:

extension String {
  func formatted(_ arguments: CVarArg...) -&gt; String {
    return String(format: self, locale: Locale.current, arguments: arguments)

That would look like this now: “BUTTON_TERMS_OF_USE”.localized.formatted(“Tom”)

Now to the attributed string itself:

extension String {
  var attributed: NSAttributedString {
    do {
      return try NSAttributedString.init(
        data: String.Encoding.utf8)!,
        options: [NSDocumentTypeDocumentAttribute: NSHTMLTextDocumentType, NSCharacterEncodingDocumentAttribute: String.Encoding.utf8.rawValue],
        documentAttributes: nil )
    } catch {
      return NSAttributedString.init(string: self)

To translate it correctly using HTML string:

If you now have to translate strings more often and don’t want to use the storyboard’s own translation or you use attributed strings, then you can extend view classes:

class LocalizedButton : UIButton {
  @IBInspectable var localizedTitle : String = "" {
      didSet {
          self.setTitle(localizedTitle.localized, for: .normal)
  @IBInspectable var attributedTitle : String = "" {
      didSet {
          self.setAttributedTitle(attributedTitle.localized.attributed, for: .normal)

Now you can use the utility editor to enter the translation ID. If there are placeholders in the text, the translation must take place in the swiftcode itself.

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