Get plurals right in every language

How to do it

Pick the message for each count from the language's plural rules. Use Intl.PluralRules in JavaScript, Babel in Python, or ICU MessageFormat in PHP and Java. Some languages have up to six forms, such as Arabic, so give translators every form the language needs.

Example

const rules = new Intl.PluralRules('en');
const msg = { one: '# file', other: '# files' };
const label = n => msg[rules.select(n)].replace('#', n);
label(1); // "1 file"
label(3); // "3 files"

# Python with Babel
from babel import Locale
english = Locale("en")
messages = {"one": "{n} file", "other": "{n} files"}
label = lambda n: messages[english.plural_form(n)].format(n=n)
label(1)  # "1 file"

// PHP with ICU MessageFormat
$files = new MessageFormatter('en', '{n, plural, one {# file} other {# files}}');
echo $files->format(['n' => 3]); // "3 files"

How to check

A unit test runs the counts 0, 1, 2, 5 and 21 for each language. Each picks the right form.