The Language does not change in the ASP.NET Core Web application

Question

I follow the Globalization and localization and Building simple multilingual ASP.NET Core website tutorials to add a language switch for my application.

So, I created a partial view

@using Microsoft.AspNetCore.Builder
@using Microsoft.AspNetCore.Http.Features
@using Microsoft.AspNetCore.Localization
@using Microsoft.AspNetCore.Mvc.Localization
@using Microsoft.Extensions.Options

@inject IViewLocalizer Localizer
@inject IOptions<RequestLocalizationOptions> LocOptions

@{
    var requestCulture = Context.Features.Get<IRequestCultureFeature>();
    var cultureItems = LocOptions.Value.SupportedUICultures
        .Select(c => new SelectListItem { Value = c.Name, Text = c.DisplayName })
        .ToList();
}

<div title="@Localizer["Request culture provider:"] @requestCulture?.Provider?.GetType().Name">
    <form id="selectLanguage" asp-controller="Home"
          asp-action="SetLanguage" asp-route-returnUrl="@Context.Request.Path"
          method="post" class="form-horizontal" role="form">
        @Localizer["Language:"] 
        <select name="culture"
                onchange="this.form.submit();"
                asp-for="@requestCulture.RequestCulture.UICulture.Name" asp-items="cultureItems"></select>
    </form>
</div>

Added in the footer of the _Layout the

<div class="col-md-6 text-right">
    @await Html.PartialAsync("_SelectLanguagePartial")
</div>

and configure the Startup.cs like this:

services.AddLocalization(options => options.ResourcesPath = "Resources");

services.AddMvc()
    .AddViewLocalization(LanguageViewLocationExpanderFormat.Suffix)
    .AddDataAnnotationsLocalization();

services.Configure<RequestLocalizationOptions>(options =>
{
    var supportedCultures = new[]
    {
        new CultureInfo("es"),
        new CultureInfo("en")
    };

    options.DefaultRequestCulture = new RequestCulture(culture: "es", uiCulture: "es");
    options.SupportedCultures = supportedCultures;
    options.SupportedUICultures = supportedCultures;    

});

I added a Resources folder and in it the

Views.Home.Index.es.resx
Views.Home.Index.en.resx
Views.Shared._Layout.es.resx
Views.Shared._Layout.en.resx

I also did Install-Package Microsoft.AspNetCore.Authentication.Cookies

When I load the Home View I have the Spanish option selected. But when I try to select "English" it loads, but rolls-back the Spanish version, so I can't finally see my content in English. Where is the problem?

Answer 1

Add an additional answer for those who did not make it work even if you have updated your code with Joe Auddette's answer.

The CookieOptions blocked me a long time to make things work:

[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),
            IsEssential = true,  //critical settings to apply new culture
            Path = "/",
            HttpOnly = false,
        }
    );

    return LocalRedirect(returnUrl);
}

IsEssential has following comments in source code:

Indicates if this cookie is essential for the application to function correctly. If true then consent policy checks may be bypassed. The default value is false.

and the consent policy is set in startup.cs

services.Configure<CookiePolicyOptions>(options =>
{
    // This lambda determines whether user consent for non-essential cookies 
    // is needed for a given request.
    options.CheckConsentNeeded = context => true;
    options.MinimumSameSitePolicy = SameSiteMode.None;
});