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Gerasimos (Makis) Maropoulos
Gerasimos (Makis) Maropoulos

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Internationalization and localization with Go

#go #localization #webdev #tutorial

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Hello Gophers!

In this article we will learn how to convert a single language web application to a multi language one.

Tools used in this article:

First of all, create a directory that hosts your application, e.g. myapp, and install Iris:

$ go mod init myapp
$ go get github.com/kataras/iris/v12@master
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Follow the tutorial below.

Internationalization and localization

Localization features provide a convenient way to retrieve strings in various languages, allowing you to easily support multiple languages within your application. Language strings are stored in files within the ./locales directory. Within this directory there should be a subdirectory for each language supported by the application:

│   main.go
└───locales
    ├───el-GR
    │       home.yml
    ├───en-US
    │       home.yml
    └───zh-CN
            home.yml
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The default language for your application is the first registered language.

app := iris.New()

// First parameter: Glob filpath patern,
// Second variadic parameter: Optional language tags,
// the first one is the default/fallback one.
app.I18n.Load("./locales/*/*", "en-US", "el-GR", "zh-CN")
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Or if you load all languages by:

app.I18n.Load("./locales/*/*")
// Then set the default language using:
app.I18n.SetDefault("en-US")
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Load embedded locales

You may want to embed locales with a go-bindata tool within your application executable.

  1. install a go-bindata tool, e.g.

$ go get -u github.com/go-bindata/go-bindata/...

  1. embed local files to your application

$ go-bindata -o locales.go ./locales/...

  1. use the LoadAssets method to initialize and load the languages

^ The AssetNames and Asset functions are generated by go-bindata

ap.I18n.LoadAssets(AssetNames, Asset, "en-US", "el-GR", "zh-CN")
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Defining Translations

Locale files can be written at YAML(recommended), JSON, TOML or INI form.

Each file should contain keys. Keys can have sub-keys(we call them "sections") too.

Each key's value should be of form string or map containing by its translated text (or template) or/and its pluralized key-values.

Iris i18n module supports pluralization out-of-the-box, see below.

Fmt Style 

hi: "Hi %s!"
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ctx.Tr("Hi", "John")
// Outputs: Hi John!
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Template 

hi: "Hi {{.Name}}!"
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ctx.Tr("Hi", iris.Map{"Name": "John"})
// Outputs: Hi John!
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Pluralization

Iris i18n supports plural variables. To define a per-locale variable you must
define a new section of Vars key.

The acceptable keys for variables are:

  • one
  • "=x" where x is a number
  • "<x"
  • other
  • format

Example:

Vars:
  - Minutes:
      one: "minute"
      other: "minutes"
  - Houses:
      one: "house"
      other: "houses"
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Then, each message can use this variable, here's how:

# Using variables in raw string
YouLate: "You are %[1]d ${Minutes} late."
# [x] is the argument position,
# variables always have priority other fmt-style arguments,
# that's why we see [1] for houses and [2] for the string argument.
HouseCount: "%[2]s has %[1]d ${Houses}."
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ctx.Tr("YouLate", 1)
// Outputs: You are 1 minute late.
ctx.Tr("YouLate", 10)
// Outputs: You are 10 minutes late.

ctx.Tr("HouseCount", 2, "John")
// Outputs: John has 2 houses.
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You can select what message will be shown based on a given plural count.

Except variables, each message can also have its plural form too!

Acceptable keys:

  • zero
  • one
  • two
  • "=x"
  • "<x"
  • ">x"
  • other

Let's create a simple plural-featured message, it can use the Minutes variable we created above too.

FreeDay:
  "=3": "You have three days and %[2]d ${Minutes} off." # "FreeDay" 3,15
  one:  "You have a day off." # "FreeDay", 1
  other: "You have %[1]d free days." # "FreeDay", 5
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ctx.Tr("FreeDay", 3, 15)
// Outputs: You have three days and 15 minutes off.
ctx.Tr("FreeDay", 1)
// Outputs: You have a day off.
ctx.Tr("FreeDay", 5)
// Outputs: You have 5 free days.
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Let's continue with a bit more advanced example, using template text + functions + plural + variables.

Vars:
  - Houses:
      one: "house"
      other: "houses"
  - Gender:
      "=1": "She"
      "=2": "He"

VarTemplatePlural:
  one: "${Gender} is awesome!"
  other: "other (${Gender}) has %[3]d ${Houses}."
  "=5": "{{call .InlineJoin .Names}} are awesome."
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const (
    female = iota + 1
    male
)

ctx.Tr("VarTemplatePlural", iris.Map{
    "PluralCount": 5,
    "Names":       []string{"John", "Peter"},
    "InlineJoin": func(arr []string) string {
        return strings.Join(arr, ", ")
    },
})
// Outputs: John, Peter are awesome

ctx.Tr("VarTemplatePlural", 1, female)
// Outputs: She is awesome!

ctx.Tr("VarTemplatePlural", 2, female, 5)
// Outputs: other (She) has 5 houses.
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Sections

If the key is not a reserved one (e.g. one, two...) then it acts as a sub section. The sections are separated by dot characters (.).

Welcome:
  Message: "Welcome {{.Name}}"
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ctx.Tr("Welcome.Message", iris.Map{"Name": "John"})
// Outputs: Welcome John
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Determining The Current Locale

You may use the context.GetLocale method to determine the
current locale or check if the locale is a given value:

func(ctx iris.Context) {
    locale := ctx.GetLocale()
    // [...]
}
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The Locale interface looks like this.

// Locale is the interface which returns from a
// `Localizer.GetLocale` metod.
// It serves the transltions based on "key" or format. See `GetMessage`.
type Locale interface {
    // Index returns the current locale index from the languages list.
    Index() int
    // Tag returns the full language Tag attached tothis Locale,
    // it should be uniue across different Locales.
    Tag() *language.Tag
    // Language should return the exact languagecode of this `Locale`
    //that the user provided on `New` function.
    //
    // Same as `Tag().String()` but it's static.
    Language() string
    // GetMessage should return translated text based n the given "key".
    GetMessage(key string, args ...interface{}) string
}
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Retrieving Translation

Use of context.Tr method as a shortcut to get a translated text for this request.

func(ctx iris.Context) {
    text := ctx.Tr("hi", "name")
    // [...]
}
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Inside Views 

func(ctx iris.Context) {
    ctx.View("index.html", iris.Map{
        "tr": ctx.Tr,
    })
}
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Thanks for reading 🙏 Have fun and be safe indoors 💪

Follow my GitHub and Twitter.

Special thanks to Damon Blais

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