ICU Message Format: Plurals, Selects, and Variables

Concatenating translated strings with variables produces grammatically incorrect results in many languages (e.g., You have 1 messages).

Use ICU message syntax to embed variables, plurals, and selects directly inside translation strings.

// messages/en.json
{
  "inbox": "You have {count, plural, =0 {no messages} one {# message} other {# messages}}",
  "greeting": "{gender, select, male {He} female {She} other {They}} liked your post.",
  "date": "Posted on {date, date, medium}"
}

// Usage with react-intl
intl.formatMessage({ id: 'inbox' }, { count: 0 })  // 'You have no messages'
intl.formatMessage({ id: 'inbox' }, { count: 1 })  // 'You have 1 message'
intl.formatMessage({ id: 'inbox' }, { count: 5 })  // 'You have 5 messages'
intl.formatMessage({ id: 'greeting' }, { gender: 'female' }) // 'She liked your post.'

ICU message format is the standard used by most professional translation tools (Phrase, Lokalise, Crowdin). It embeds translation logic inside the string so translators can see the full context and adjust plural forms for their language.