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Cocoaheads August 2012 - 2.key Add the keynote file new link

/* Melbourne Cocoheads August 2012 presentation title */
"talk-title" = "Localising your apps.";

/* presentation author */
"presentation-by" = "Jesse Collis";

/* presentation author email address */
"author-email" = "";


Three stages of localisation

  1. Initial development
  2. Initial localisation effort
  3. Ongoing updates

If your Localizable.strings file looks like this but you're lazy

/* No comment provided by engineer. */
"Next" = "Next";

The absolute worst localisation offenders

The "Oh I heard literal strings in code are bad" kind of localisation

NSLocalizedString(@"Next", @"");
NSLocalizedString(@"Next", nil);

The wtf is the comment for anyway kind of localisation

NSLocalizedString(@"Next", @"Next");

The out of sight out of mind kind of localisation

#define MYBadCompanyLocalizedString(key) NSLocalizedString((key), @"")

The entire book as a key kind of localisation

NSLocalizedString(@"In order to determine your location, location services must be turned on in settings", @"In order to determine your location, location services must be turned on in settings");

The key can be anything but I know what it is kind of localisation

NSString *aStringFromAPI = [response objectForKey:@"next-title"];
NSLocalizedString(aStringFromAPI, @"api resposne for `next`");

In this case Apple's tools can't help you; genstrings will throw warnings and ignore your NSLocalizedString() all together.

The not as bad offenders

Duplicating keys

This is a grey area; good comments can make duplicating keys manageable

NSLocalizedString(@"Next", @"RootViewController 'next' button title");
NSLocalizedString(@"Next", @"DetailViewController 'next page' button title");

Good comments show you the key's appearances in your app in the .strings file

/* DetailViewController 'next page' button title
   RootViewController 'next' button title */
"Next" = "Next";
  • genstrings will warn you about duplicate keys
  • Bad/stupid/empty comments make this a bad offender
  • keys with nil or @"" comments aren't picked up as duplicate

Using localised strings in format strings

button.titleLabel.text = [NSString stringWithFormat:@"4 %@, 3 %@", 
                          NSLocalizedString(@"pineapples",@"plural pineapples"),
                          NSLocalizedString(@"pears",@"plural pears")];

This is grey area because it's inflexible and implies a structure, but can be okay for really small strings, but often you should consider NSNumberFormatter for numbers. (That's another talk)

Localising the format string too

button.titleLabel.text = [NSLocalizedString stringWithFormat:
                          NSLocalizedString(@"4 %@, 3 %@", @"fruit quantities format string"),
                          NSLocalizedString(@"pineapples",@"plural pineapples"),
                          NSLocalizedString(@"pears",@"plural pears")];

But at this point we've got localised pieces everywhere. But it's good that you're trying.

How NSLocalizedString() works

NSLocalizedString() macros all call to NSBundle

#define NSLocalizedString(key, comment) \
        [[NSBundle mainBundle] localizedStringForKey:(key) value:@"" table:nil]
#define NSLocalizedStringFromTable(key, tbl, comment) \
        [[NSBundle mainBundle] localizedStringForKey:(key) value:@"" table:(tbl)]
#define NSLocalizedStringFromTableInBundle(key, tbl, bundle, comment) \
        [bundle localizedStringForKey:(key) value:@"" table:(tbl)]
#define NSLocalizedStringWithDefaultValue(key, tbl, bundle, val, comment) \
        [bundle localizedStringForKey:(key) value:(val) table:(tbl)]

- (NSString *)localizedStringForKey:(NSString *) value:(NSString *) table:(NSString *)

localizedStringForKey:value:table: has defaults

  • default table is Localizable
  • default value is nil or @""
  • unlocalized keys return vale or the key if value is nil

NSBundle's localisation selection

You can localise resources by duplicating them in *.lproj directories. You can see the supported localisations as an array of string in your NSBundle instance has with:

NSArray *localisations = [bundle localizations];

po [[NSBundle mainBundle] localizations]
(id) $4 = 0x08356290 <__NSCFArray 0x8356290>(en,ko)

These folders must be of a particular format. en / english, ko / Korean. You can't just give it random .lproj folder names. .lproj directory names` should be canonicalized IETF BCP 47 language identifier strings. Here's a list

NSBundle then references the @"AppleLanguages" key from [NSUserDefaults standardUserDefaults] in combination with it's - localizations to work out what .lproj directory it will look for key: and table:.

My educated guess is the @"AppleLanguages" key in NSUserDefaults is derived from [NSLocale preferredLocalizations] which represents your system's preferred localisations in order of preference.

po [[NSUserDefaults standardUserDefaults] objectForKey:@"AppleLanguages"];
(id) $1 = 0x0754e790 <__NSCFArray 0x754e790>(

There is a number of Stack Overflow posts on how to force NSLocalizedString() to use a language by changing this value in NSUserDefaults early in the app lifecycle, even changing it, syncing it and force quitting the app.

There's also some smarts here about what to look for if nothing is localised, but it's not that important here.

Within localizedStringForKey:value:table

At this point we're looking for a stringsTable based on the set localisation which we know already is just an IETF BCP 47 NSString.

To find our strings table path we use another NSBundle method:

NSString *tablePath = [bundle pathForResource:tableName 

To translate this path from a .strings file into something we can use, we use:

NSString *stringsFile = [NSString stringWithContentsOfFile:stringsFilePath 

NSDictionary *stringsDict = [stringsFile propertyListFromStringsFileFormat];

And finally, where key is the original key we passed to NSLocalizedString():

return [stringsDict objectForKey:key];


From NSString.h regarding propertyListFromStringsFileFormat

These methods are no longer recommended since they do not work with property lists and strings files in binary plist format. Please use the APIs in NSPropertyList.h instead.

My way to use NSLocalizedString()

self.title = NSLocalizedStringFromTable(@"nav-title",@"StationDetailController",@"NavigationItem title (Station Detail)");

Use the longer NSLocalizedStringFromTable()

Provide a tableName to each string.

This splits your .strings files by logical sections making localisation easier and implies a context to your keys and comments.

Use unique keys

Even with the extra context provided by the different table names, I'm an advocate for unique keys across everything.


Provide useful comments with the suggested English (en) localisation included

@"NavigationItem title (Station Detail)"

@"TableView section 2 ('Other City Metro apps')"

Localising format strings

Here's how not to do it

overviewCell.detail = [NSString stringWithFormat:
NSLocalizedString(@"stops and transfers format",@"Format for saying (1- 15) (3- stops) and (2- 4) (4-Transfers)"),
[NSNumber numberWithInt:[self.route.routePath count] - 1],
[NSNumber numberWithInt:[self.route.transfers count] - 1],
[self.route.transfers count] > 1 ? 
  NSLocalizedString(@"Transfers",@"Plural transfers") : 
  NSLocalizedString(@"Transfer",@"Singular Transfers")];

Don't do this... localise each case

if (stops > 1){
  if (transfers > 1){
    detailString = [NSString stringWithFormat:NSLocalizedStringFromTable(@"plural-stops-plural-transfers",@"RouteDetail",@"Overview Header - 2 (plural) stops and 2 (plural) transfers ('%@ stops and %@ transfers')"), stopsNumber, transfersNumber];
  }else if (transfers == 1){
    detailString = [NSString stringWithFormat:NSLocalizedStringFromTable(@"plural-stops-single-transfer",@"RouteDetail",@"Overview Header - 2 (plural) stops and 1 (singular) transfer ('%@ stops and %@ transfer')"), stopsNumber, transfersNumber];
    detailString = [NSString stringWithFormat:NSLocalizedStringFromTable(@"plural-stops",@"RouteDetail",@"Overview Header - 2 (plural) stops ('%@ stops')"), stopsNumber];
  detailString = JCLocalizedStringFromTable(@"one-stop",@"RouteDetail",@"Overview Header - 1 (singular) stop ('only one stop!')");

Localising non-literal strings

If you've got strings from API or external source that aren't statically defined, genstrings complains, as it can't read your keys.

My solution is to use a specific table and use genstrings -skipTable to skip it so it won't error, and will let me create my own .strings file.

NSLocalizedStringFromTable(apiValue, @"ApiTranslations", @"apiValue for such and such");

Using genstrings properly

  • Use genstring -s to define your own macros. Make sure their name doesn't clash with other class names.
  • If you use *stringFromTable: it will create the appropriate .strings file for you
  • It will read NSLocalizedString* elements in comments
  • Output your files to any directory, like en.lproj
  • It gives good good warnings
  • suppress multiple key warnings with -q
  • It will add numbers to format string parameters @1$% etc
  • You can skip certain tableNames with -skipTable (see localising non-literals)


    genstrings -s JCLocalizedString ./*.m -o ./en.lproj

Localising xibs and story boards with ibtool

generate your strings

ibtool --generate-strings-file MainStoryboard.strings MainStoryboard.storyboard

write your strings

ibtool --strings-file ~/MainStoryboard.strings 
       --write ../ko.lproj/MainStoryboard.storyboard MainStoryboard.storyboard

Xcode 4.4 , Mountain Lion, iOS 6 lets you localise a xib file with a .strings file named the same.

Show non localised strings with -NSShowNonLocalizedStrings

Pass -NSShowNonLocalizedStrings YES as a launch argument in your scheme and see the unlocalised strings come to life in ALLCAPS

Supporting your app going forward

The previous info is great when you build an app from scratch, but updating an app months or years after initial release means your strings change, contexts change and this is hard to manage, especially if you use some of the bad methods above.


  • Manages your strings files, and changes.
  • A smarter wrapper around genstrings and libtool


AppCode has blazed ahead in this space

Their latest blog post details a lot of new features

  • Rename localisation keys
  • Provide missing localisations
  • Highlight unused keys
  • Find usage of a key

Localisation services

Other Third Party Tools

  • Greenwich

Extensions to this talk

  • Auto Layout OSX Lion, iOS 6
  • Internationalisation with NSLocale, NSDateFormatter, NSNumberFormatter

Other References

WWDC Session 244 'Internationalization tips and tricks' presented by Dave De Long

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