How do I format dates for different locales in EK9?

← Date, Time, and Duration · Ref: Q549

EK9's Locale type provides four named formatting levels that automatically adapt to regional conventions. No format pattern strings needed.

FOUR FORMATTING LEVELS FOR DATES

  shortFormat: compact numeric (03/10/2020 GB, 10/3/20 US)
  mediumFormat: abbreviated month (Oct 3, 2020 US, 3 Oct 2020 GB)
  longFormat: full month name (3. Oktober 2020 DE)
  fullFormat: includes day-of-week (Samstag, 3. Oktober 2020 DE)

Each locale adjusts automatically: date order (day/month vs month/day), separators, month names, and day names.

SAME METHODS FOR TIME AND DATETIME

The four formatting levels also work on Time and DateTime:

  locale.shortFormat(09:30:00) gives locale-appropriate time
  locale.longFormat(2024-06-15T10:30:00Z) gives full date+time+timezone

DAY OF WEEK

  locale.dayOfWeek(date) returns the localized day name:
  Locale('de_DE').dayOfWeek(2024-06-15) gives 'Samstag'
  Locale('en_GB').dayOfWeek(2024-06-15) gives 'Saturday'

WHY NO PATTERN STRINGS

Pattern strings like 'yyyy-MM-dd' or 'dd/MM/yyyy' are error-prone: 'mm' means minutes in Java but months in Excel. Named levels are unambiguous and locale-correct by default.

See Q44 for the complete Locale formatting guide. See Q537 for ISO 8601 formatting. See Q551 for RFC 7231 HTTP date headers.

Example

defines module qa.locale.date.formatting

  defines program
    LocaleDateFormattingDemo()
      stdout <- Stdout()

      wedding <- 2020-10-03
      lunchTime <- 12:00:01
      meeting <- 2024-06-15T10:30:00Z

      // Create locales
      enGB <- Locale("en_GB")
      enUS <- Locale("en_US")
      deutsch <- Locale("de_DE")
      francais <- Locale("fr_FR")

      // Date formatting - four levels
      stdout.println("=== Date Formatting ===")
      stdout.println(`GB short: ${enGB.shortFormat(wedding)}`)
      stdout.println(`US short: ${enUS.shortFormat(wedding)}`)
      stdout.println(`GB medium: ${enGB.mediumFormat(wedding)}`)
      stdout.println(`US medium: ${enUS.mediumFormat(wedding)}`)
      stdout.println(`DE long: ${deutsch.longFormat(wedding)}`)
      stdout.println(`FR long: ${francais.longFormat(wedding)}`)
      stdout.println(`GB full: ${enGB.fullFormat(wedding)}`)
      stdout.println(`DE full: ${deutsch.fullFormat(wedding)}`)

      // Time formatting
      stdout.println("=== Time Formatting ===")
      stdout.println(`GB short time: ${enGB.shortFormat(lunchTime)}`)
      stdout.println(`US short time: ${enUS.shortFormat(lunchTime)}`)
      stdout.println(`DE medium time: ${deutsch.mediumFormat(lunchTime)}`)

      // DateTime formatting
      stdout.println("=== DateTime Formatting ===")
      stdout.println(`US short DT: ${enUS.shortFormat(meeting)}`)
      stdout.println(`GB medium DT: ${enGB.mediumFormat(meeting)}`)
      stdout.println(`DE long DT: ${deutsch.longFormat(meeting)}`)
      stdout.println(`FR full DT: ${francais.fullFormat(meeting)}`)

      // Day of week
      stdout.println("=== Day of Week ===")
      stdout.println(`GB: ${enGB.dayOfWeek(wedding)}`)
      stdout.println(`DE: ${deutsch.dayOfWeek(wedding)}`)
      stdout.println(`FR: ${francais.dayOfWeek(wedding)}`)

Common mistakes

E50060 — Locale has no generic format() method. Use the four named methods: shortFormat(), mediumFormat(), longFormat(), fullFormat(). See ek9 -h E50060 for details.

Incorrect:

stdout.println(`GB short: ${enGB.format(wedding, "short")}`)

Correct:

stdout.println(`GB short: ${enGB.shortFormat(wedding)}`)

Other ways to ask this

How do I display dates in German or French format?
How do locale formatting levels work with dates?
How do I internationalize date display?

Coming from another language?

Java: DateTimeFormatter.ofLocalizedDate(FormatStyle.SHORT).withLocale(). Python: babel.dates.format_date(style='short', locale='de_DE'). JavaScript: Intl.DateTimeFormat with options. Go: no built-in locale formatting. Rust: no built-in, chrono-locale crate. EK9: Locale('de_DE').shortFormat(date) four named levels, no pattern strings.

Keywords: time, mediumFormat, locale, regional, format, dayOfWeek, internationalization, duration, date, shortFormat, i18n, timezone, migrate, longFormat, fullFormat