go-i18n is a Go package and a command that helps you translate Go programs into multiple languages.

• Supports pluralized strings for all 200+ languages in the Unicode Common Locale Data Repository (CLDR).
  • Code and tests are automatically generated from CLDR data.
• Supports strings with named variables using text/template syntax.
• Supports message files of any format (e.g. JSON, TOML, YAML).

The i18n package provides support for looking up messages according to a set of locale preferences.

import "github.com/nicksnyder/go-i18n/v2/i18n"

Create a Bundle to use for the lifetime of your application.

bundle := i18n.NewBundle(language.English)

Load translations into your bundle during initialization.

bundle.RegisterUnmarshalFunc("toml", toml.Unmarshal)
bundle.LoadMessageFile("es.toml")

Create a Localizer to use for a set of language preferences.

func(w http.ResponseWriter, r *http.Request) {
    lang := r.FormValue("lang")
    accept := r.Header.Get("Accept-Language")
    localizer := i18n.NewLocalizer(bundle, lang, accept)
}

Use the Localizer to lookup messages.

localizer.Localize(&i18n.LocalizeConfig{
    DefaultMessage: &i18n.Message{
        ID: "PersonCats",
        One: "{{.Name}} has {{.Count}} cat.",
        Other: "{{.Name}} has {{.Count}} cats.",
    },
    TemplateData: map[string]interface{}{
        "Name": "Nick",
        "Count": 2,
    },
    PluralCount: 2,
}) // Nick has 2 cats.

The goi18n command manages message files used by the i18n package.

go get -u github.com/nicksnyder/go-i18n/v2/goi18n
goi18n -help

Use goi18n extract to extract all i18n.Message struct literals in Go source files to a message file for translation.

# active.en.toml
[PersonCats]
description = "The number of cats a person has"
one = "{{.Name}} has {{.Count}} cat."
other = "{{.Name}} has {{.Count}} cats."

1. Create an empty message file for the language that you want to add (e.g. translate.es.toml).

2. Run goi18n merge active.en.toml translate.es.toml to populate translate.es.toml with the mesages to be translated.