Number Formatting in ICU Messages

Locale-Aware Number Formatting

The number argument type in ICU MessageFormat formats numeric values according to the rules of the target locale. This handles thousands separators, decimal points, currency symbols, and percentage formatting automatically.

Basic Number Formatting

{count, number}

Locale	Input	Output
en-US	1234567.89	1,234,567.89
de-DE	1234567.89	1.234.567,89
ja-JP	1234567.89	1,234,567.89
fr-FR	1234567.89	1 234 567,89

Number Styles

ICU defines several built-in number styles:

Currency

The total is {amount, number, currency}.

Locale	Input	Output
en-US	42.5	$42.50
de-DE	42.5	42,50 EUR
ja-JP	42.5	43 JPY

Currency formatting adapts symbol placement, decimal digits, and the currency code based on the locale.

Percent

Completion: {ratio, number, percent}

Locale	Input	Output
en-US	0.856	86%
fr-FR	0.856	86 %

Note: The input value is treated as a fraction (0.856 = 85.6%), not as a percentage already.

Integer

About {count, number, integer} items

Rounds to the nearest integer:

• 42.7 -> 43
• 42.2 -> 42

In Sentences

Combine number formatting with surrounding text:

Your cart: {itemCount, number} {itemCount, plural, one {item} other {items}} totaling {total, number, currency}.

With itemCount=3 and total=149.99 in en-US: "Your cart: 3 items totaling $149.99."

Why Not Format in Code?

Formatting numbers in application code before passing them to the message breaks the localization contract. The translator has no control over how numbers appear in different locales. Always pass raw numeric values and let the ICU formatter handle locale-specific formatting.

Custom Number Patterns

Some ICU implementations support custom number patterns using Unicode number format syntax:

{amount, number, ::currency/EUR}
{ratio, number, ::.00}

However, support for custom patterns varies by library. The standard styles (currency, percent, integer) are universally supported.