Test an ICU message in any locale

What ICU MessageFormat is

ICU MessageFormat is a syntax for messages that change with their arguments. A placeholder is {name}; a formatted one adds a type, such as {size, number} or {date, date, long}; and the complex arguments, plural, selectordinal and select, pick a sub-message. Plural categories (zero, one, two, few, many, other) come from CLDR, the same data behind the Pluralization Tester. Exact matches like =0 are checked before the categories, and # prints the number formatted for the locale: 1,234 in English, 1.234 in German.

Reading the example, piece by piece

• {name} is a simple argument: the value is inserted as-is.
• {count, plural, =0 {no files} one {# file} other {# files}} checks the exact value 0 first, then asks CLDR for the category. With 1234 that is other, and # becomes "1,234" in English and "1.234" in German.
• {size, number, ::unit/megabyte unit-width-short} is a number skeleton. ICU picks the unit abbreviation for the locale: "52.5 MB" in English, "52,5 Mo" in French.
• {gender, select, female {her} male {his} other {their}} chooses by exact string. Any value you did not list, including a missing one, lands on other.
• {date, date, long} formats a date in the locale's long style: "March 14, 2026" in English, "14. März 2026" in German.

The comparison table runs your pattern unchanged in seven locales. The words do not translate themselves, but everything ICU controls does: digit grouping, decimal separators, unit names, date order and which plural branch is chosen. That makes it a quick way to spot a branch you forgot for one of your target languages.

ICU and Laravel

Laravel's translator does not understand ICU syntax. __() swaps :placeholders with a plain string replacement, and trans_choice() picks pipe-separated forms with its own rule table in MessageSelector, not CLDR. You can see the difference with the trans_choice() Tester. If you want ICU messages in a Laravel app, the intl extension gives you the formatter directly:

// lang/en/files.php
'shared' => '{count, plural, =0 {No files} one {# file} other {# files}}',

// anywhere
$message = MessageFormatter::formatMessage(
    app()->getLocale(),
    __('files.shared'), // no replacements, so Laravel returns the line untouched
    ['count' => $files->count()],
);

Call __() without a replacement array, so Laravel hands back the raw pattern and ICU does all the work. Laravel's Number helper already depends on the same extension: Number::format() and Number::currency() throw if intl is missing. ICU accepts both pt-BR and pt_BR, unlike Laravel's plural table.

Mistakes ICU will and will not catch

• Missing other: every plural and select needs an other branch. Without it, ICU refuses the pattern with U_DEFAULT_KEYWORD_MISSING.
• Unbalanced braces: reported as U_PATTERN_SYNTAX_ERROR with the offset where parsing stopped.
• Missing arguments: not an error. Hi {name} without a name renders as "Hi {name}", which is why this page lists them.
• Apostrophes: a single quote before a brace starts a quoted literal, so '{n}' prints {n}. Write '' for a literal quote there. An apostrophe inside a word, as in "I'm", is left alone.
• Forgotten categories: a Polish message with only one and other parses fine, but 22 needs few. Set the locale of the first example to pl: 1,234 falls in the few category, which that pattern does not define, so ICU uses other.