Add translation example

[cxlblm]

No description provided.

[coveralls]

coverage: 73.653% (+0.05%) from 73.607%
when pulling 6b3ea1d on cxlblm:translation
into 0540a5e on go-playground:master.

[nodivbyzero]

Thanks for your contribution to the project.

Where is zhTrans being used?

[cxlblm]

Thanks for your contribution to the project.

Where is zhTrans being used?

The variable zhTrans exists to register the global Chinese translator using zh_translations.RegisterDefaultTranslations(validate, zhTrans). This is done to ensure that both English (en) and Chinese (zh) can be supported in the future.

[nodivbyzero]

Hmm....
When I execute this example, the Chinese translation doesn't appear.

$ cd _examples/translations && go run main.go
map[User.Tagline:Tagline must be less than 10 characters in length User.Tagline2:Tagline2 must be greater than 1 character in length]
Username is a required field
Username must have a value!

[cxlblm]

Hmm.... When I execute this example, the Chinese translation doesn't appear.

$ cd _examples/translations && go run main.go
map[User.Tagline:Tagline must be less than 10 characters in length User.Tagline2:Tagline2 must be greater than 1 character in length]
Username is a required field
Username must have a value!

The purpose of en_translations.RegisterDefaultTranslations(validate, enTrans) and zh_translations.RegisterDefaultTranslations(validate, zhTrans) is to pre-register all supported languages. However, the specific language to be used is determined by the accept-language in the HTTP header. For simplicity, a fixed value (uni.GetTranslator("en")) is hardcoded in the code. Below is a demo from our real-world scenario.

package main

import (
	"encoding/json"
	"errors"
	"github.com/go-playground/locales/en"
	"github.com/go-playground/locales/zh"
	ut "github.com/go-playground/universal-translator"
	"github.com/go-playground/validator/v10"
	en_translations "github.com/go-playground/validator/v10/translations/en"
	zh_translations "github.com/go-playground/validator/v10/translations/zh"
	"net/http"
)

var uni *ut.UniversalTranslator

func main() {
	validate := validator.New()
	en := en.New()
	uni = ut.New(en, en, zh.New())

	validate = validator.New()
	enTrans, _ := uni.GetTranslator("en")
	en_translations.RegisterDefaultTranslations(validate, enTrans)
	zhTrans, _ := uni.GetTranslator("zh")
	zh_translations.RegisterDefaultTranslations(validate, zhTrans)

	type User struct {
		FirstName string `json:"first_name" validate:"required"`
		LastName  string `json:"last_name" validate:"required"`
	}

	http.HandleFunc("POST /users", func(w http.ResponseWriter, r *http.Request) {
		// ... fill user value
		var user User

		// Header Accept-Language value is en or zh
		trans, _ := uni.GetTranslator(r.Header.Get("Accept-Language"))
		if err := validate.Struct(&user); err != nil {
			var errs validator.ValidationErrors
			var httpErrors []validator.ValidationErrorsTranslations
			if errors.As(err, &errs) {
				httpErrors = append(httpErrors, errs.Translate(trans))
			}
			r, _ := json.Marshal(httpErrors)
			w.Write(r)
		}
	})

	http.ListenAndServe(":8081", nil)
}

[nodivbyzero]

This ☝️ type of example is highly valuable. I’d include it in this PR as a separate function, possibly with a client http request that sets the Accept-Language header to 'zh'.

[cxlblm]

I tried executing your example, but it resulted in the following error:

main.go:8:2: cannot find module providing package github.com/go-playground/locales/zh_Hant:

Would you be able to fix it?

Could you provide the execution environment? It works fine on my local machine. Could you also check whether the relevant packages are present?

[nodivbyzero]

Here you go:

$ git clean -ffdx
$ go mod vendor
$ cd _examples/http-transalations 
$ go run main.go
main.go:8:2: cannot find module providing package github.com/go-playground/locales/zh_Hant

[cxlblm]

Here you go:

$ git clean -ffdx
$ go mod vendor
$ cd _examples/http-transalations 
$ go run main.go
main.go:8:2: cannot find module providing package github.com/go-playground/locales/zh_Hant

I pinpointed the issue and found that the dependency related to zh_Hant wasn't included during compilation, which caused go mod vendor to skip copying the relevant dependencies into the vendor directory. I’ve adjusted the dependencies accordingly. However, I’m curious—what's the purpose of using the go mod vendor command in the first place?

[nodivbyzero]

4a3f92e fixes the dependency issue. I'm able to run your example.

How can I see the localized error message?
I attempted a POST request, but it returned the following output:

curl -d '{"first_name":"foo"}' -H "Accept-Language: zh-TW" -H "Content-Type: application/json" -X POST http://localhost:8081/users

[{"User.FirstName":"FirstName is a required field","User.LastName":"LastName is a required field"}]

[cxlblm]

4a3f92e fixes the dependency issue. I'm able to run your example.

How can I see the localized error message? I attempted a POST request, but it returned the following output:

curl -d '{"first_name":"foo"}' -H "Accept-Language: zh-TW" -H "Content-Type: application/json" -X POST http://localhost:8081/users

[{"User.FirstName":"FirstName is a required field","User.LastName":"LastName is a required field"}]

You can use the following command to get error messages in Traditional Chinese:

curl -d '{"first_name":"foo"}' -H "Accept-Language: zh-Hant-TW" -H "Content-Type: application/json" -X POST http://localhost:8081/users

Or use this command to get messages in Simplified Chinese:

curl -d '{"first_name":"foo"}' -H "Accept-Language: zh" -H "Content-Type: application/json" -X POST http://localhost:8081/users