Use localized strings in storyboard

I think being able to localise Strings in the storyboard is of significant advantage. I don't agree with @elk_cloner that hooking up IBOutlets for every UILabel is the way forward.

One way of getting it to work is using an @IBInspectable property on a UILabel subclass:

class LocalisableLabel: UILabel {

    @IBInspectable var localisedKey: String? {
        didSet {
            guard let key = localisedKey else { return }
            text = NSLocalizedString(key, comment: "")
        }
    }

}

In the storyboard set the custom class:

In the attributes inspector the localisedKey field will appear and you can just add your key here.

That's it!

EDIT:

You can localise UIButtons the same way, BUT if the text in the storyboard's title field differs from the localised String (which it will in other languages) the setting of the title will animate.

To fix this, put the setTitle in a performWithoutAnimation block:

class LocalisableButton: UIButton {

    @IBInspectable var localisedKey: String? {
        didSet {
            guard let key = localisedKey else { return }
            UIView.performWithoutAnimation {
                setTitle(key.localized, for: .normal)
                layoutIfNeeded()
            }
        }
    }

}

According to your requirement it's not possible but

You don't need different storyboards for localization

Suppose you want to localize a label string.

1. Draw and outlet and change text using

mylabel.text = nsLocalizedString("THIS_IS_MY_STRING",nil);

Of course in your localization file there will be a line.You must have different files for different language.Suppose you have a file for english and there must be a line.

"THIS_IS_MY_STRING" = "This is my string";

When you compile your app, that function will use mapping to localize your app.

Edit:

If you want detail information please have a look at these tutorials internationalization-tutorial-for-ios-2014

and ios-localization-tutorial

There are some online script(e.g localize.py) which will help you to automatically search all of your code and find out nslocalizedString function and make lines in your localizableString files. like this.

"THIS_IS_MY_STRING" = "THIS_IS_MY_STRING"

and later on you just have to write actual string there. :)

In addition to Leon's answer, you can get rid of the need for an explicit subclass by using an extension:

extension UILabel {
    @IBInspectable var localizableText: String? {
        get { return text }
        set(value) { text = NSLocalizedString(value!, comment: "") }
    }
}