Add translation example

[cxlblm]

No description provided.

[coveralls]

coverage: 74.466%. remained the same
when pulling 59d14ea on cxlblm:translation
into bae7f6d 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]

Alright, I'm not very familiar with GitHub's collaboration workflow. Thank you so much for promptly handling this.

[nodivbyzero]

@cxlblm Could you update this PR by adding a new example subfolder that includes your working code from above?