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Localization in Xamarin.iOS

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This document covers the localization features of the iOS SDK and how to access them with Xamarin.

Refer to the Internationalization Encodings for instructions on including character sets/code pages in applications that must process non-Unicode data.

iOS platform features

This section describes some of the localization features in iOS. Skip to the next section to see specific code and examples.

Language

Users choose their language in the Settings app. This setting affects the language strings and images displayed by the operating system and in apps.

To determine the language being used in an app, get the first element of NSBundle.MainBundle.PreferredLocalizations:

var lang = NSBundle.MainBundle.PreferredLocalizations[0];

This value will be a language code such as en for English, es for Spanish, ja for Japanese, etc. The value returned is restricted to one of the localizations supported by the application (using fallback rules to determine the best match).

Application code does not always need to check for this value – Xamarin and iOS both provide features that help to automatically provide the correct string or resource for the user's language. These features are described in the remainder of this document.

Note

Use NSLocale.PreferredLanguages to determine the user's language preferences, regardless of the localizations supported by the app. The values returned by this method changed in iOS 9; see Technical Note TN2418 for details.

Locale

Users choose their locale in the Settings app. This setting affects the way that dates, times, numbers, and currency are formatted.

This lets users choose whether they see 12-hour or 24-hour time formats, whether their decimal separator is a comma or a point, and the order of day, month and year in date display.

With Xamarin you have access to both Apple’s iOS classes (NSNumberFormatter) as well as the .NET classes in System.Globalization. Developers should evaluate which is better suited to their needs, as there are different features available in each. In particular, if you are retrieving and displaying In-App Purchase prices using StoreKit you should use Apple’s formatting classes for the price information returned.

The current locale can be queried by either of two ways:

  • NSLocale.CurrentLocale.LocaleIdentifier
  • NSLocale.AutoUpdatingCurrentLocale.LocaleIdentifier

The first value can be cached by the operating system and so might not always reflect the user’s currently selected locale. Use the second value to obtain the currently selected locale.

Note

Mono (the .NET runtime upon which Xamarin.iOS is based) and Apple’s iOS APIs do not support identical sets of language/region combinations. Because of this, it’s possible to select a language/region combination in the iOS Settings app that does not map to a valid value in Mono. For example, setting an iPhone’s language to English and its region to Spain will cause the following APIs to yield different values:

  • CurrentThead.CurrentCulture: en-US (Mono API)
  • CurrentThread.CurrentUICulture: en-US (Mono API)
  • NSLocale.CurrentLocale.LocaleIdentifier: en_ES (Apple API)

Since Mono uses CurrentThread.CurrentUICulture to select resources and CurrentThread.CurrentCulture to format dates and currencies, Mono-based localization (for example, with .resx files) may not yield expected results for these language/region combinations. In these situations, rely on Apple's APIs to localize as necessary.

NSCurrentLocaleDidChangeNotification

iOS generates an NSCurrentLocaleDidChangeNotification when the user updates their locale. Applications can listen for this notification while they are running and can make appropriate changes to the UI.

Localization basics in iOS

The following features of iOS are easily leveraged in Xamarin to provide localized resources for display to the user. Refer to the TaskyL10n sample to see how to implement these ideas.

Specifying default and supported languages in Info.plist

In Technical Q&A QA1828: How iOS Determines the Language For Your App, Apple describes how iOS selects a language to use in an app. The following factors impact which language is displayed:

  • The user's preferred languages (found in the Settings app)
  • The localizations bundled with the app (.lproj folders)
  • CFBundleDevelopmentRegion (Info.plist value specifying the default language for the app)
  • CFBundleLocalizations (Info.plist array specifying all supported localizations)

As indicated in the Technical Q&A, CFBundleDevelopmentRegion represents an app's default region and language. If the app doesn't explicitly support any of a user's preferred languages, it will use the language specified by this field.

Important

iOS 11 applies this language selection mechanism more strictly than did previous versions of the operating system. Because of this, any iOS 11 app that does not explicitly declare its supported localizations – either by including .lproj folders or setting a value for CFBundleLocalizations – may display a different language in iOS 11 than it did in iOS 10.

If CFBundleDevelopmentRegion has not been specified in the Info.plist file, the Xamarin.iOS build tools currently use a default value of en_US. While this may change in a future release, it means that the default language is English.

To ensure that your app selects an expected language, take the following steps:

  • Specify a default language. Open Info.plist and use the Source view to set a value for the CFBundleDevelopmentRegion key; in XML, it should look similar to the following:
<key>CFBundleDevelopmentRegion</key>
<string>es</string>

This example uses “es” to specify that when none of a user’s preferred languages are supported, default to Spanish.

  • Declare all supported localizations. In Info.plist, use the Source view to set an array for the CFBundleLocalizations key; in XML, it should look similar to the following:
<key>CFBundleLocalizations</key>
<array>
    <string>en</string>
    <string>es</string>
    ...
</array>

Xamarin.iOS apps that have been localized using .NET mechanisms such as .resx files must provide these Info.plist values as well.

For more information about these Info.plist keys, take a look at Apple's Information Property List Key Reference.

GetLocalizedString method

The NSBundle.MainBundle.GetLocalizedString method looks up localized text that has been stored in .strings files in the project. These files are organized by language, in specially named directories with an .lproj suffix (note the first letter of the extension is a lower-case "L").

.strings file locations

  • Base.lproj is the directory that contains resources for the default language. It is often located in the project root (but can also be placed in the Resources folder).
  • <language>.lproj directories are created for each supported language, usually in the Resources folder.

There can be a number of different .strings files in each language directory:

  • Localizable.strings – the main list of localized text.
  • InfoPlist.strings – certain specific keys are allowed in this file to translate things such as the application name.
  • <storyboard-name>.strings – optional file that contains translations for user interface elements in a storyboard.

The Build Action for these files should be Bundle Resource.

.strings file format

The syntax for localized string values is:

/* comment */
"key"="localized-value";

You should escape the following characters in strings:

  • \" quote
  • \\ backslash
  • \n newline

This is an example es/Localizable.strings (ie. Spanish) file from the sample:

"<new task>" = "<new task>";
"Task Details" = "Detalles de la tarea";
"Name" = "Nombre";
"task name" = "nombre de la tarea";
"Notes" = "Notas";
"other task info"= "otra información de tarea";
"Done" = "Completo";
"Save" = "Guardar";
"Delete" = "Eliminar";

Images

To localize an image in iOS:

  1. Refer to the image in code, for example:

    UIImage.FromBundle("flag");

  2. Place the default image file flag.png in Base.lproj (the native development language directory).

  3. Optionally place localized versions of the image in .lproj folders for each language (eg. es.lproj, ja.lproj). Use the same filename flag.png in each language directory.

If an image is not present for a particular language, iOS will fall back to the default native language folder and load the image from there.

Launch images

Use the standard naming conventions for the launch images (and the XIB or Storyboard for iPhone 6 models) when placing them in the .lproj directories for each language.

Default.png
Default@2x.png
Default-568h@2x.png
LaunchScreen.xib

App name

Placing an InfoPlist.strings file in an .lproj directory lets you override some values from the app's Info.plist, including the application name:

"CFBundleDisplayName" = "LeónTodo";

Other keys that you can use to localize application-specific strings are:

  • CFBundleName
  • CFBundleShortVersionString
  • NSHumanReadableCopyright

Dates and times

Although it is possible to use the built-in .NET date and time functions (along with the current CultureInfo) to format dates and times for a locale, this would ignore locale-specific user-settings (which can be set separately from language).

Use the iOS NSDateFormatter to produce output that matches the user's locale preference. The following sample code demonstrates the basic date and time formatting options:

var date = NSDate.Now;
var df = new NSDateFormatter ();
df.DateStyle = NSDateFormatterStyle.Full;
df.TimeStyle = NSDateFormatterStyle.Long;
Debug.WriteLine ("Full,Long: " + df.StringFor(date));
df.DateStyle = NSDateFormatterStyle.Short;
df.TimeStyle = NSDateFormatterStyle.Short;
Debug.WriteLine ("Short,Short: " + df.StringFor(date));
df.DateStyle = NSDateFormatterStyle.Medium;
df.TimeStyle = NSDateFormatterStyle.None;
Debug.WriteLine ("Medium,None: " + df.StringFor(date));

Results for English in the United States:

Full,Long: Friday, August 7, 2015 at 10:29:32 AM PDT
Short,Short: 8/7/15, 10:29 AM
Medium,None: Aug 7, 2015

Results for Spanish in Spain:

Full,Long: viernes, 7 de agosto de 2015, 10:26:58 GMT-7
Short,Short: 7/8/15 10:26
Medium,None: 7/8/2015

Refer to the Apple Date Formatters documentation for more information. When testing locale-sensitive date and time formatting, check both iPhone Language and Region settings.

Right-to-Left (RTL) layout

iOS provides a number of features to assist in building RTL-aware apps:

  • Use auto layout's leading and trailing attributes for control alignment (which corresponds to left and right for English, but is reversed for RTL languages). The UIStackView control is particularly useful for laying out controls to be RTL-aware.
  • Use TextAlignment = UITextAlignment.Natural for text alignment (which will be left for most languages but right for RTL).
  • UINavigationController automatically flips the back button and reverses swipe direction.

The following screenshots show the localized Tasky sample in Arabic and Hebrew (although English has been entered in the fields):

Localization in Arabic

Localization in Hebrew

iOS automatically reverses the UINavigationController, and the other controls are placed inside UIStackView or aligned with Auto-Layout. RTL text is localized using .strings files in the same way as LTR text.

Localizing the UI in code

The Tasky (localized in code) sample shows how to localize an application where the user-interface is built in code (rather than XIBs or storyboards).

Project Structure

Screenshot shows the resources tree for a sample including the location of localizable strings.

Localizable.strings file

As described above, the Localizable.strings file format consists of key-value pairs. The key describes the intent of the string and the value is the translated text to be used in the app.

The Spanish (es) localizations for the sample are shown below:

"<new task>" = "<new task>";
"Task Details" = "Detalles de la tarea";
"Name" = "Nombre";
"task name" = "nombre de la tarea";
"Notes" = "Notas";
"other task info"= "otra información de tarea";
"Done" = "Completo";
"Save" = "Guardar";
"Delete" = "Eliminar";

Performing the localization

In the application code, wherever a user interface's display text is set (whether it is a label's text, or an input's placeholder, etc) the code uses the iOS GetLocalizedString function to retrieve the correct translation to display:

var localizedString = NSBundle.MainBundle.GetLocalizedString ("key", "optional");
someControl.Text = localizedString;

Localizing storyboard UIs

The sample Tasky (localized storyboard) shows how to localize text on controls in a storyboard.

Project structure

The Base.lproj directory contains the storyboard, and should also contain any images used in the application.

The other language directories contain a Localizable.strings file for any string resources referenced in code, as well as a MainStoryboard.strings file that contains translations for text in the storyboard.

Screenshot shows the resources tree for a sample including the location of MainStoryboard strings.

The language directories should contain a copy of any images that have been localized, to override the one present in Base.lproj.

Object ID / Localization ID

When creating and editing controls in a storyboard, select each control and check the ID to use for localization:

  • In Visual Studio for Mac, it's located in the Properties Pad and is called Localization ID.
  • In Xcode, it's called Object ID.

This string value often has a form such as "NF3-h8-xmR", as shown in the following screenshot:

Xcode view of Storyboard localization

This value is used in the .strings file to assign translated text automatically to each control.

MainStoryboard.strings

The format of the storyboard translation file is similar to the Localizable.strings file, except that the key (the value on the left) cannot be user-defined but instead must have a very specific format: ObjectID.property.

In the example Mainstoryboard.strings below you can see UITextFields have a placeholder text property that can be localized; UILabels have a text property; and UIButtons default text is set using normalTitle:

"SXg-TT-IwM.placeholder" = "nombre de la tarea";
"Pqa-aa-ury.placeholder"= "otra información de tarea";
"zwR-D9-hM1.text" = "Detalles de la tarea";
"bAM-2j-Rzw.text" = "Notas";           /* Notes */
"NF3-h8-xmR.text" = "Completo";        /* Done */
"MWt-Ya-pMf.normalTitle" = "Guardar";  /* Save */
"IGr-pR-05L.normalTitle" = "Eliminar"; /* Delete */

Important

Using a storyboard with size classes may result in translations that do not appear in the application. Apple's Xcode Release Notes indicate that a storyboard or XIB will not localize correctly if three things are true: it uses size classes, the base localization and the build target are set to Universal, and the build targets iOS 7.0. The fix is to duplicate your storyboard strings file into two identical files: MainStoryboard~iphone.strings and MainStoryboard~ipad.strings, as shown in the following screenshot:

Strings files

App Store listing

Follows Apple's FAQ on App Store Localization to enter translations for each country your app is on sale. Note their warning that the translations will only appear if your app also contains a localized .lproj directory for the language.

Summary

This article covers the basics of localizing iOS applications using the built-in resource handling and storyboard features.

You can learn more about i18n and L10n for iOS, Android and cross-platform apps (including Xamarin.Forms) in this cross-platform guide.