Tiny useful wrapper function of NSLocalizedString in Swift

EasyLocalization.swift

//
//  EasyLocalization.swift
//
//  Created by Doba Duc on 9/1/15.
//  Copyright (c) 2015 Doba Duc. All rights reserved.
//

/// Tiny useful wrapper function of NSLocalizedString in Swift
///
/// @param key Localizable key
/// @param replacements (Optional) A dictionary of replacements to be used in a formatted string.
/// @return Localized string

func lang(key: String, _ replacements: [String: String]? = [:]) -> String {
    if let dict = replacements {
        var string = NSLocalizedString(key, comment: "")
        for (k, v) in dict {
            string = string.stringByReplacingOccurrencesOfString("#{\(k)}", withString: v)
        }
        return string
    } else {
        return NSLocalizedString(key, comment: "")
    }
}

// Assume that your Localizable.strings file looks like below:
//      "user.name.format" = "Mr./Ms. #{name}"  // Placeholder format: #{<placeholder_key>}
//      "welcome.text" = "Welcome to Swift world!"
//      ...
//      ...

// Usage examples:
print(lang("welcome.text"))
print(lang("user.name.format", ["name": "Smith"]))

The example below shows why we need this wrapper around NSLocalizedString and String(format:arguments) function calls to handle localized texts more efficiently.

(Just copy & paste the following code blocks to a playground and see the results)

Handling localized texts as usual

var format = NSLocalizedString("sentence_format", comment: "") // Retrieve the format from strings table

// EN: 
format = "A %@ has %d %@s" // This line is just to make the example work without strings files
var englishText = String(format: format, arguments: ["cat", 4, "leg"]) // --> "A cat has 4 legs"

// JA:
format="%@は%@が%d本あります"
var japaneseText = String(format: format, arguments: ["猫", "足", 4]) // --> "猫は足が4本あります"

Issue with the code above:

• Can't use the same argument array for any languages due to the grammatical differences
• Need to pay attention on the type of each argument

In the example above, we can't just write a single line of code that works for both English and Japanese!

let localizedText = String(format: NSLocalizedString("sentence_format", comment: ""), [value1, value2, value3])

Handling localized texts with the wrapper function

func lang(key: String, _ replacements: [String: String]? = [:]) -> String {
    if let dict = replacements {
        var string = NSLocalizedString(key, comment: "")
        for (k, v) in dict {
            string = string.stringByReplacingOccurrencesOfString("#{\(k)}", withString: v)
        }
        return string
    } else {
        return NSLocalizedString(key, comment: "")
    }
}

format = "A #{animal} has #{number} #{organ}s"
var englishText2 = lang(format, ["animal": "cat", "number": "4", "organ": "leg"])  // --> "A cat has 4 legs"

format = "#{animal}は#{organ}が#{number}本あります"
var japaneseText2 = lang(format, ["animal": "猫", "number": "4", "organ": "足"]) // "猫は足が4本あります"

Advantages:

• No needs to care about argument types or orders
• Use exactly the same formatting code for any languages
• Write shorter code instead calling both NSLocalizedString and String(format:arguments)

In short, write 1 single line of code for any languages and let the wrapper handle the rest

let localizedText = lang("sentence_format", ["animal": animalName, "number": numberOfOrgan, "organ": organName])