Internationalization

govalid is locale-aware end-to-end: rule messages, field labels and diagnostic templates can all be localized.

Bundled locales

Locale	Tag
Chinese (default)	language.Chinese
English	language.English

The default locale is Chinese. Override it by setting govalid.defaultTemplateLanguage is not exposed — pick a locale per call instead.

Per-call locale

Check accepts an optional language.Tag:

import "golang.org/x/text/language"

errs, ok := govalid.Check(form, language.English)

Selection rules:

1. Use the requested locale's template set if it exists.
2. If the locale isn't registered, fall back to the package default (Chinese).
3. If a specific template key is missing inside the chosen locale, fall back to _unknownErrorTemplate.

Localized field labels

label-<lang> tags let you attach per-locale labels alongside the default label tag. The lang suffix matches language.Tag.String():

type Form struct {
    Email string `valid:"required" label:"邮箱" label-en:"Email"`
}

govalid.Check(form, language.English) // → "Email can not be empty"
govalid.Check(form, language.Chinese) // → "邮箱不能为空"

Lookup order per call:

1. label-<lang> for the requested locale
2. label
3. The Go field name

Adding a new locale

SetMessageTemplates creates the locale on first use:

import "golang.org/x/text/language"

govalid.SetMessageTemplates(map[string]string{
    "required": " は必須です",
    "min":      " は %v 以上である必要があります",
}, language.Japanese)

You can override entries selectively — only the keys you provide are replaced; the rest fall back to the default locale per the rules above.

Choosing a locale at runtime

A common pattern is to derive the locale from an HTTP request:

func handler(w http.ResponseWriter, r *http.Request) {
    var form Form
    _ = json.NewDecoder(r.Body).Decode(&form)

    matcher := language.NewMatcher([]language.Tag{
        language.Chinese, language.English, language.Japanese,
    })
    accept, _, _ := language.ParseAcceptLanguage(r.Header.Get("Accept-Language"))
    tag, _, _ := matcher.Match(accept...)

    errs, ok := govalid.Check(form, tag)
    if !ok {
        // render `errs` to the client
    }
}

Diagnostic templates by locale

The five _-prefixed diagnostic templates are localized too. Override them per locale just like regular rule templates:

govalid.SetMessageTemplates(map[string]string{
    "_checkerNotFound":      "Unknown rule",
    "_paramError":           "Bad rule parameters",
    "_valueTypeError":       "Wrong field type",
    "_fieldNotFound":        "Referenced field not found",
    "_unknownErrorTemplate": "Validation failed",
}, language.English)