TYPO3 Core

This feature implements support of plural forms in language files. Units in XLIFF files can be grouped to define plural forms of a translation:

<group id="day" restype="x-gettext-plurals">
  <trans-unit id="day[0]">
    <source>%1$s day</source>
  </trans-unit>
  <trans-unit id="day[1]">
    <source>%1$s days</source>
  </trans-unit>
</group>

The number in [] defines the plural form as defined here: http://docs.translatehouse.org/projects/localization-guide/en/latest/l10n/pluralforms.html
Behaviour of existing TYPO3 installations is not changed. To make use of the plural forms a new argument named quantity is introduced and handed all the way down from TranslateViewHelper over LocalizationUtility::translate to LanguageService->sL. TranslationService->translate supports the new argument, too.
If no quantity value is passed, the form [0] is used as default.
Examples:

<f:translate id="my.label" quantity="1" />
<f:translate arguments="{0: quantity}" id="my.label" quantity="{quantity}" />
$languageService->sL($id, 42);

At the suggestion of Georg Ringer, the ContentObjectRenderer also received support for this feature. The argument can be appended to the label in TypoScript seperated by a comma.
Example:

label = TEXT
label.data = LLL:EXT:my_ext/Resources/Private/Language/locallang.xlf:my.label,42

Translation cache takes the plural forms into account.