Locales

Locales

Go-gui's locale system controls number formatting, date formatting, currency display, and UI string translation. Locales are values — register them, switch at runtime, and use the formatting helpers wherever you display locale-sensitive data.

---

The Locale type

type Locale struct {
    ID             string         // e.g. "en-US", "de-DE"
    Label          string         // human-readable label
    NumberFormat   NumberFormat   // digit grouping, decimal/group separators
    DateFormat     DateFormat     // short/long date patterns, first day of week
    CurrencyFormat CurrencyFormat // symbol, code, position, decimal places
    Translations   map[string]string
}

The zero-value Locale{} uses en-US defaults (period decimal, comma grouping, M/D/YYYY dates, USD currency).

---

Number formatting

NumberFormat controls how numbers are displayed:

type NumberFormat struct {
    GroupSizes []int // default [3]
    DecimalSep rune  // default '.'
    GroupSep   rune  // default ','
    MinusSign  rune  // default '-'
    PlusSign   rune  // default '+'
}

Use gui.LocaleFormatFloat64(v, decimals, lc) or gui.LocaleFormatInt64(n, lc) to format numbers for display:

lc, _ := gui.LocaleGet("de-DE")
s := gui.LocaleFormatFloat64(1234567.89, 2, lc)
// "1.234.567,89"

---

Date formatting

DateFormat controls date patterns and calendar conventions:

type DateFormat struct {
    ShortDate      string // "M/D/YYYY" or "DD.MM.YYYY"
    LongDate       string // "MMMM D, YYYY" or "D. MMMM YYYY"
    MonthYear      string // "MMMM YYYY"
    FirstDayOfWeek uint8  // 0=Sunday, 1=Monday
    Use24H         bool
}

Format a date with gui.LocaleFormatDate(t, format):

lc, _ := gui.LocaleGet("de-DE")
s := gui.LocaleFormatDate(time.Now(), lc.DateFormat.ShortDate)
// "14.06.2026"

Pattern tokens: YYYY (4-digit year), MM / M (month, zero-padded or not), DD / D (day), HH, mm, ss. Month names come from the locale's translations map ("January", "Jan", etc.).

---

Currency formatting

type CurrencyFormat struct {
    Symbol   string               // "$", "€", "¥"
    Code     string               // "USD", "EUR", "JPY"
    Position NumericAffixPosition // AffixPrefix or AffixSuffix
    Spacing  bool                 // true adds a space between symbol and amount
    Decimals int                  // 2
}

Use gui.LocaleFormatCurrency(amount float64, lc Locale) to format a monetary value.

---

Built-in locales

Go-gui ships preset locale data for:

Locale ID	Language / Region
en-US	English (United States) — the default
de-DE	German (Germany)
es-ES	Spanish (Spain)
fr-FR	French (France)
he-IL	Hebrew (Israel)
ja-JP	Japanese
ko-KR	Korean
pt-BR	Portuguese (Brazil)
zh-CN	Chinese (Simplified)
ar-SA	Arabic (Saudi Arabia)

---

Registering and looking up locales

Presets auto-register at init. Add your own:

gui.LocaleRegister(gui.Locale{
    ID:     "en-GB",
    Label:  "English (UK)",
    DateFormat: gui.DateFormat{
        ShortDate:      "DD/MM/YYYY",
        LongDate:       "D MMMM YYYY",
        MonthYear:      "MMMM YYYY",
        FirstDayOfWeek: 1, // Monday
        Use24H:         false,
    },
    CurrencyFormat: gui.CurrencyFormat{
        Symbol:   "£",
        Code:     "GBP",
        Position: gui.AffixPrefix,
        Decimals: 2,
    },
    Translations: map[string]string{
        "January": "January",
        "Feb":     "Feb",
        // ... fill in all month/weekday keys
    },
})

lc, ok := gui.LocaleGet("en-GB")

gui.LocaleRegisteredNames() []string returns sorted IDs of all registered locales. Use it to populate a locale picker.

---

Loading locales from files

gui.LocaleLoadDir(dir string) error reads all *.json files from a directory and registers each as a locale. File names should match locale IDs (e.g. de-DE.json).