Localizing Dynamic Plural Noun messages (e.g. "5 Items Processed") on iPhone using Objective-C

As of iOS 7, Foundation framework has native support for pluralization.Here is a quick tutorial how to use it:

Create a plist file named as Localizable.stringsdict

English Localization:

<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd"><plist version="1.0">    <dict>        <key>%d tasks waiting for action</key>        <dict>            <key>NSStringLocalizedFormatKey</key>            <string>%#@tasks@ waiting for action</string>            <key>tasks</key>            <dict>                <key>NSStringFormatSpecTypeKey</key>                <string>NSStringPluralRuleType</string>                <key>NSStringFormatValueTypeKey</key>                <string>d</string>                <key>one</key>                <string>A task is</string>                <key>two</key>                <string>Two tasks are</string>                <key>other</key>                <string>%d tasks are</string>            </dict>        </dict>    </dict></plist>

Polish Localization:

<?xml version="1.0" encoding="UTF-8"?><!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd"><plist version="1.0">    <dict>        <key>%d tasks waiting for action</key>        <dict>            <key>NSStringLocalizedFormatKey</key>            <string>Masz %#@zadanie@ do zrobienia</string>            <key>zadanie</key>            <dict>                <key>NSStringFormatSpecTypeKey</key>                <string>NSStringPluralRuleType</string>                <key>NSStringFormatValueTypeKey</key>                <string>d</string>                <key>one</key>                <string>jedno zadanie</string>                <key>few</key>                <string>%d zadania</string>                <key>other</key>                <string>%d zadań</string>            </dict>        </dict>    </dict></plist>

And finally in your implementation file, you can call the dictionary like this:

cell.tasksInfoLabel.text = [NSString localizedStringWithFormat:NSLocalizedString(@"%d tasks waiting for action", @"%d tasks waiting for action"), (long)taskCount];

EDIT:Thanks Zaphod for pointing this out ->: You also need to create the Localizable.strings file alongside the .stringsdict to have the pluralization work (even if it's empty).

My team developed an open source library for handling just this situation, checkout our iOS i18n plural library on github.

The basic premise is that the keys for plural strings are extended to contain their plural form according to the CLDR plural rules and the lookup of the strings does not use the typical NSLocalizedString.

The English file for the example posted would look like this:

"%d Items Processed##{one}"   = "1 Item Processed";    "%d Items Processed##{other}" = "%d Items Processed";

The lookup would then be done using a SLPluralizedString function

SLPluralizedString(@”%d Items Processed”, numItems, @”Number of items processed”);

At runtime, for English the String "1 Item Processed" or "%d Items Processed" would be returned depending on the value of numItems.

The Russian file would then look like this:

"%d Items Processed##{one}"   = "%d элемент обработан";"%d Items Processed##{few}"   = "%d элемента обработано";"%d Items Processed##{many}"  = "%d элементов обработано";"%d Items Processed##{other}" = "%d элемента обработано";

Your code then to lookup "Items Processed" for Russian or any other language wouldn't have to change and the library would return the correct String according to the CLDR plural rules for that particular language.

Please feel free to share your thoughts on the library, suggestions, improvements, etc.

In English, there are just 2 plural forms, e.g. "1 file" and "5 files". In Russian, there are 3 plural forms (101 файл, 2 файла, 11 файлов), unless you count non-integers. Actually, there can actually be up to 6 plural forms in a language (e.g. Arabic has 6) . There seems to be 3 ways to deal with the problem, just choose whatever is good enough but not too complicated for you:

1. Try to use plural-neutral messages, e.g. "Number of items processed: %d" instead of "%d item processed | %d items processed ".

2. Support localizations for each plural form, up to 6.

   "%d Gold Coins##{PluralForm0}" -> "%d золотая монета" // e.g. 1 gold coin"%d Gold Coins##{PluralForm1}" -> "%d золотые монеты" // e.g. 2 gold coins"%d Gold Coins##{PluralForm2}" -> "%d золотых монет"  // e.g. 5 gold coins…"%d Gold Coins##{PluralForm5}" -> "%d How did we get here if this is not Arabic???"

   Knowing the value of %d and the target language, you app will have to detect the plural form number in the runtime, i.e. implement something like

   unsigned int "NumberToPluralFormNumber(unsigned int number, const std::string& langCode);

   method. If you support just 2-5 languages and the numbers in the messages are always non-negative ints, it is actually quite simple to implement it w/o any 3d party lib, you can copy/paste C-compatible one-liners for each language from http://docs.translatehouse.org/projects/localization-guide/en/latest/l10n/pluralforms.html . Please note that it's valid for non-negative integers only, so the number of plural forms might differ from what unicode.org says.

3. 3d party libs.