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Localization In .NetCore MVC Application

Localization:

The translation to a specific region or country or culture or local. The websites with localization can reach a wider range of audiences.

Create A DotNet Core MVC Sample Application:

Let's learn localization steps by implementing them in a sample MVC application.


Add Sample Language Collection To AppSettings File:

In our sample let's read the different languages that we support from the appSettings.json file.
appSettings.Development.json:
"LanguageCodes": [
{
  "Name": "Spain",
  "Code": "es"
},
{
  "Name": "Mexico",
  "Code": "es-Mx"
},
{
  "Name": "United States",
  "Code": "en-us"
}
]
Let's create a type for the "LanguageCodes".
Shared/LanguageCodes:
namespace Sample.Localization.Mvc.Shared
{
  public class LanguageCodes
  {
    public string Name { get; set; }
    public string Code { get; set; }
  }
}
Register the 'LangaugeCodes' Type in DI(Dependency Injection) services so that it can be accessed by injection.
Startup.cs:(ConfigureServices method)
services.Configure<List<LanguageCodes>>(Configuration.GetSection("LanguageCodes"));

UseRequestLocalization Middleware:

The current culture on request is set in the localization middleware(UseRequestLocalization Middleware). This middleware initializes the RequestLocalization object. On every request, middleware can read the current culture with the following type of providers.
  • QueryStringRequestCultureProvider.
  • CookieRequestCultureProvider.
  • AcceptLanguageHeaderRequestCultureProvider.
From the above providers, we need to understand that 'UseRequestLocalization' middleware tries to read the culture value from the 'query parameter' or 'cookie' or 'accept headers' as per the order we defined above.
Startup.cs:
private RequestLocalizationOptions RegisterSuportCulture()
{
  var langCodes = Configuration.GetSection("LanguageCodes").GetChildren().ToList().Select(_ => new LanguageCodes
  {
	Name = _.GetValue<string>("Name"),
	Code = _.GetValue<string>("Code")
  }).ToList();
  var localizationOptions = new RequestLocalizationOptions()
  .SetDefaultCulture(langCodes.Where(_ => _.Name == "United States")
  .Select(_ => _.Code).FirstOrDefault());
	
  return localizationOptions;
}
  • The 'UseRequestLocalization' middleware needs the 'Microsoft.AspNetCore.Builder.RequesLocalizationOption' object. The 'RequesLocalizationOption' object is used to configure all the cultures supported by our application.
  • (Line: 3-7) Reding the culture info from the 'appSettings.Development.json' file.
  • (Line: 9-11) Initialized RequestLocalizationOptions object by setting the default culture for the application.
Now register the 'UseRequestLocalization' middleware above the 'UseRouting' middleware.
Startup.cs:
app.UseRequestLocalization(RegisterSuportCulture());
app.UseRouting();

UI Dropdown To Change Culture:

In _Layout.cshtml we will configure a dropdown in the menu section to change the culture of the website.

Let's create a partial view to implement the dropdown functionality.
Views/Shared/_LanguageSelectionPartial.cshtml:
@using Microsoft.Extensions.Options
@using Sample.Localization.Mvc.Shared
@using Microsoft.AspNetCore.Localization;
@inject IOptions<List<LanguageCodes>> _languageCodes
@{
    var requestCulture = Context.Features.Get<IRequestCultureFeature>();
    var cultureName = requestCulture.RequestCulture.Culture.Name;
    var selectionItems = _languageCodes.Value.
        Select(_ => new SelectListItem {
            Text = _.Name,
            Value = _.Code,
            Selected = (_.Code.ToLower() == cultureName.ToLower()) }).ToList();
    var returnUrl = string.IsNullOrEmpty(Context.Request.Path) ? "~/" : $"~{Context.Request.Path.Value}";

}

<form id="selectLanguage" 
      asp-controller="Home" 
      asp-action="SetLanguage" 
      method="post" 
      class="form-horizontal" 
      role="form" 
      asp-route-returnUrl="@returnUrl"  >
    <select class="form-control" 
            name="culture" id="culture" 
            onchange="this.form.submit()" asp-items="selectionItems">
    </select>
</form>
  • (Line: 4) Injecting 'LanguageCodes' collection to display them in the dropdown.
  • (Line: 6) Creating an instance of the 'Microsoft.AspNetCore.Localization.IRequestCultureFeature'.
  • (Line: 7) Fetching the current culture of the application, by default it will 'United States' as we configured in the middleware.
  • (Line: 9-12) Creating dropdown item collection.
  • (Line: 13) The current application path will be passed as a post parameter on changing the dropdown value.
  • (Line: 17-28) The Html form that gets post values on changing the dropdown values. The 'asp-controller' and 'asp-action' attributes define endpoint(which we create in the next step) to post the form.
  • The 'asp-route-{your_parameter}' to pass the return URL as post value.

Culture And UI-Culture:

Dotnet supports two culture info objects like 'culture' and 'ui-culture'. The 'culture' is for translation of the text to display. The 'ui-culture' is for translation of date, time, numbers, and currency.

So we have to configure providers like 'SupportedCultures' and 'SupportedUICultures' to the RequesLocalizationOption object. So let's update our 'RegisterSuportCulture' method in the startup class.
Startup.cs:(Update RegisterSuportCulture method)
private RequestLocalizationOptions RegisterSuportCulture()
{
  var langCodes = Configuration.GetSection("LanguageCodes").GetChildren().ToList().Select(_ => new LanguageCodes
  {
	Name = _.GetValue<string>("Name"),
	Code = _.GetValue<string>("Code")
  }).ToList();
  var supportedCultures = langCodes.Select(_ => _.Code).ToArray();
  var localizationOptions = new RequestLocalizationOptions().SetDefaultCulture(langCodes.Where(_ => _.Name == "United States").Select(_ => _.Code).FirstOrDefault())
  .AddSupportedCultures(supportedCultures)
  .AddSupportedUICultures(supportedCultures);
  return localizationOptions;
}
  • (Line: 8) Creating an array of cultures.
  • (Line: 10-11) The 'AddSupportedCultures' and 'AddSupportedUICultures' configured.

MVC Endpoint Query Param Culture Redirection:

Create an MVC endpoint that get's invoked on dropdown change, this endpoint redirects us with a query parameter contains the value of the culture. Our query parameter should be like 'culture'(translation for text), 'ui-culture'(translation for the date, time, currency etc).
Controllers/HomeController.cs:
[HttpPost]
public IActionResult SetLanguage(string culture, string returnUrl)
{
  returnUrl = $"{returnUrl}?ui-culture={culture}&culture={culture}";
  return LocalRedirect(returnUrl);
}

Test UI-Culture Translation:

Let's test UI-Culture translation by adding test data on index.cshtml.
Views/Home/index.cshtml:
<h5>@DateTime.Now.ToShortDateString()</h5>
 <h5>@(Convert.ToDouble("1777.00").ToString("C2", System.Globalization.CultureInfo.CurrentCulture))</h5>

Resource File:

A resource file contains a translated string for our localization. An example of the resource file is like 'Example.resx'.

The resource file name should be fully qualified for its namespace by excluding the library name. For example, we have 'TestLocalization.dll' and we can create a resource file based on Stratup.cs file like Startup.resx,  Startup.es.resx(contains Spanish translated string). Another example of creating a resource file for HomeContorller can be done with dot notation or folder notation. Coming dot notation file names look like 'Controllers.HomeController.resx', 'Controllers.HomeController.es.resx'. Coming to folder notation file names like 'Resources/Controllers/HomeController.resx', 'Resources/Controllers/HomeController.es.resx'. Similarly, we can create resource files in views(*.cshtml) level also.

Configure Localization Service:

In the Startup.cs file add the following service for accessing and identifying the resource files localization.
Startup.cs:(Inside ConfigureServices Methods)
services.AddLocalization(options => options.ResourcesPath = "Resources");
services.
AddControllersWithViews()
.AddViewLocalization(LanguageViewLocationExpanderFormat.Suffix);
  • (Line: 1) Giving instruction to check for the resource file inside the 'Resources' folder.
  • (Line: 2) This helps to check files with culture suffix example files like 'Example.es.resx'(es culture suffix).

Culture Change Using IStringLocalizer:

The IStringLocalizer<T> has the capability to load the translated string based on culture. It has the capability to choose the resource file name based on the culture.
Controllers/HelloWorldController.cs:
using Microsoft.AspNetCore.Mvc;
using Microsoft.Extensions.Localization;

namespace Sample.Localization.Mvc.Controllers
{
  public class HelloWorldController : Controller
  {
	private readonly IStringLocalizer<HelloWorldController> _stringLocalizer;
	public HelloWorldController(IStringLocalizer<HelloWorldController> stringLocalizer)
	{
		_stringLocalizer = stringLocalizer;
	}
	public IActionResult Index()
	{
		ViewData["Message"] = _stringLocalizer["Hello World"];
		return View();
	}
  }
}
  • (Line: 15) The 'Hello World' will be the key value of the resource file.
Here implemented resource files using dot notation as below.
For default culture no need to prefix the resource file. Here in our sample default culture is English.
Views/HelloWorld.Index.cshtml:
<h5>@ViewData["Message"]</h5>

Culture Change Using IHtmlLocalizer:

The IHtmlLocalizer has the capability to load the translated string along with Html tags in it.
Controllers/GoodMorningController.cs:
using Microsoft.AspNetCore.Mvc;
using Microsoft.AspNetCore.Mvc.Localization;

namespace Sample.Localization.Mvc.Controllers
{
  public class GoodMorningController : Controller
  {
	private readonly IHtmlLocalizer<GoodMorningController> _htmlLocalizer;
	public GoodMorningController(IHtmlLocalizer<GoodMorningController> htmlLocalizer)
	{
		_htmlLocalizer = htmlLocalizer;
	}
	public IActionResult Index()
	{
		ViewData["Message"] = _htmlLocalizer["Good Morning"];
		return View();
	}
  }
}
Views/GoodMorning/Index.cshtml:
<div>
    @ViewData["Message"]
</div>
Here for this sample, we create resource files in the folder structure.


Culture Change Using IViewLocalizer:

The 'IViewLocalizer' is an interface injectable in views to load the translated string from the resource files.
Views/GoodMorning/Index.cshtml:
@using Microsoft.AspNetCore.Mvc.Localization
@inject IViewLocalizer _viewLocalizer;
 
<div>
    @_viewLocalizer["Good Morning"]
</div>
Here also we created resource file using folder notation as below.

Use Cookie For Culture Change:

Till now we have used query params to change the state of the culture, now we will update our sample to use cookie to save the culture info.
Controllers/HomeController.cs:(Update SetLanguage Action Method)
[HttpPost]
public IActionResult SetLanguage(string culture, string returnUrl)
{
  Response.Cookies.Append(
   CookieRequestCultureProvider.DefaultCookieName,
   CookieRequestCultureProvider.MakeCookieValue(new RequestCulture(culture)),
   new CookieOptions { Expires = DateTimeOffset.UtcNow.AddYears(1) }
  );
  return LocalRedirect(returnUrl);
}
That's all about the different approaches to make an application localizable.

Wrapping Up:

Hopefully, I think this article delivered some useful information on the localizing an AspNetCore Mvc application. I love to have your feedback, suggestions, and better techniques in the comment section below.

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