Plurali, genere e formattazione dei messaggi ICU

Translating an app is more than swapping words. Different languages pluralize, gender, and order words differently. A naive string like "$count items" reads wrong as "1 items", and many languages have several plural forms.

Flutter solves this with ICU message syntax (International Components for Unicode), the same standard used across the industry. You write one message with rules for plurals, select/gender, and placeholders, and the right form is chosen at runtime per locale.

• plural — pick a form based on a number
• select — pick a branch based on a string (e.g. gender)
• placeholders — inject typed values like names, dates, numbers

Flutter's flutter_localizations + intl toolchain reads ARB files (Application Resource Bundle). Each locale has its own file: app_en.arb, app_tr.arb, etc.

An ARB entry has a key, a value (the ICU message), and an optional @key metadata object describing placeholders.

• Keys become generated Dart getters/methods.
• The @key block declares each placeholder's type and optional format.

A placeholder is written in curly braces inside the message: {name}. The generated Dart code becomes a method whose parameter matches the placeholder name.

After enabling generate: true in pubspec.yaml and running flutter gen-l10n, you call it through AppLocalizations.

The plural form picks a branch based on a number argument. Syntax: {count, plural, ...categories...}.

ICU plural categories are =0, =1, zero, one, two, few, many, other. The other branch is mandatory — it is the fallback when no other category matches. Use # to print the number itself.

• =0, =1 match the exact value.
• one, few, many are language-defined categories (English only uses one and other).

The generated method takes the count argument. The framework selects the correct branch for the active locale automatically.

Notice that English only ever needs one/other, but a locale like Polish or Arabic will use few/many in its own ARB file — your Dart call site does not change.

A common confusion: =1 is an exact value match, while one is a language plural category. They are not the same.

• =1 matches only the literal number 1.
• one matches whatever the locale's CLDR rules call the "one" category. In English that is just 1, but in some locales the one category also covers values like 21, 31, etc.

Best practice: provide other always; add one for natural singular/plural; use =0/=1 only when you need special wording ("empty", "no messages") that differs from the grammatical plural.

The select form branches on a string value rather than a number. The classic use is grammatical gender, which changes pronouns and verb agreement in many languages.

Syntax: {gender, select, male{...} female{...} other{...}}. Like plural, other is required as the fallback (and handles unknown/non-binary values gracefully).

You don't need Flutter to understand the intl primitives. The Intl.select function mirrors what the generated code does: it maps a key to a branch with an other fallback.

This standalone program shows the selection logic, including the fallback when an unexpected value arrives.

ICU lets you nest a plural inside a select (or vice versa) to handle messages that vary by both gender and count. Place one block inside a branch of the other.

Keep nesting shallow — deeply nested messages are painful for translators. If it gets complex, consider splitting into separate keys.

Placeholders can be formatted per locale using the format field in metadata. Numbers use formats like decimalPattern or currency; dates use DateFormat skeletons such as yMMMd.

This means 1234.5 renders as 1,234.5 in en-US but 1.234,5 in many European locales — automatically.

The same intl formatters power those ARB format fields. Here is a runnable program using NumberFormat and DateFormat directly, the way the generated localization code does under the hood.

You need a message that says "no messages", "1 message", or "N messages" depending on a count, and you want it to also work correctly in locales with few/many categories. Which approach is correct?

You now know how to localize dynamic text in Flutter with ICU message syntax:

• ARB files hold messages per locale; @key metadata declares placeholder types and formats.
• Placeholders {name} inject typed values into messages.
• plural {count, plural, =0{} =1{} other{}} picks a form by number; other is mandatory and # prints the value.
• =1 vs one: exact-value match versus language plural category — use exact matches only for special wording.
• select {gender, select, male{} female{} other{}} branches on a string; great for gender.
• Nesting combines gender and count when needed.
• format metadata + NumberFormat/DateFormat render numbers and dates per locale.

Write messages so translators control wording per language while your Dart call sites stay unchanged.