ASP.Net Core: set default culture from controller

Question

I am trying to set up localization in my ASP.Net Core Web API project.

I did some research and understand that there is a localization middleware with predefined request culture providers (which in my case are not acceptable), so I need to write a custom request culture provider, something like

public class CustomCultureProvider : RequestCultureProvider
{
    public override async Task<ProviderCultureResult> ChangeCulture(HttpContext httpContext)
    {
        // Return a culture...
        return new ProviderCultureResult("en-US");
    }
}

What I don't understand is how I can change the culture from a controller, that is, when an endpoint is called.

Answer 1

Here is a working demo for asp.net core 3.x that could switch three languages to display the response:

1.Custom RouteDataRequestCultureProvider:

public class CustomRouteDataRequestCultureProvider : RequestCultureProvider
{
    public int IndexOfCulture;
    public override Task<ProviderCultureResult> DetermineProviderCultureResult(HttpContext httpContext)
    {
        if (httpContext == null)
            throw new ArgumentNullException(nameof(httpContext));
        string culture = null;


        var twoLetterCultureName = httpContext.Request.Path.Value.Split('/')[IndexOfCulture]?.ToString();

        if (twoLetterCultureName == "de" )
            culture = twoLetterCultureName;
        else if (twoLetterCultureName == "fr")
            culture = twoLetterCultureName;
        else if(twoLetterCultureName =="en")
            culture = twoLetterCultureName;

        if (culture == null)
            return NullProviderCultureResult;          

        var providerResultCulture = new ProviderCultureResult(culture);

        return Task.FromResult(providerResultCulture);
    }
}

2.Startup.cs:

// This method gets called by the runtime. Use this method to add services to the container.
public void ConfigureServices(IServiceCollection services)
{
    services.AddLocalization(options => options.ResourcesPath = "Resources");

    services.AddControllers().AddViewLocalization(
    LanguageViewLocationExpanderFormat.Suffix,
    opts => { opts.ResourcesPath = "Resources"; })
    .AddDataAnnotationsLocalization();

    services.Configure<RequestLocalizationOptions>(options => {
        var supportedCultures = new CultureInfo[] {
            new CultureInfo("en"),
            new CultureInfo("de"),
            new CultureInfo("fr")
    };
        options.DefaultRequestCulture = new RequestCulture("en");
        options.SupportedCultures = supportedCultures;
        options.SupportedUICultures = supportedCultures;

        options.RequestCultureProviders = new[]{ new CustomRouteDataRequestCultureProvider{
            IndexOfCulture=1,
        }};
    });                      
}

// This method gets called by the runtime. Use this method to configure the HTTP request pipeline.
public void Configure(IApplicationBuilder app, IWebHostEnvironment env)
{
    if (env.IsDevelopment())
    {
        app.UseDeveloperExceptionPage();
    }
    var options = app.ApplicationServices.GetService<IOptions<RequestLocalizationOptions>>();
    app.UseRequestLocalization(options.Value);

    app.UseHttpsRedirection();

    app.UseRouting();

    app.UseAuthorization();
    app.UseEndpoints(endpoints =>
    {
        endpoints.MapControllers();
        endpoints.MapControllerRoute("LocalizedDefault", "{culture:cultrue}/{controller=Home}/{action=Index}/{id?}");

    });          
}

Test the project:

1.Create folder Resources/Controllers.

2.Create resource file and named as [ControllerName].[Language].resx like below:

3.Edit the content of resource file(i.e. ValuesController.de.resx):

4.Create a Controller:

[Route("{culture?}/api/[controller]")]
public class ValuesController : Controller
{
    private readonly IStringLocalizer<ValuesController> _localizer;

    public ValuesController(IStringLocalizer<ValuesController> localizer)
    {
        _localizer = localizer;
    }
    // GET: api/<controller>
    [HttpGet]
    public IActionResult Get()
    {
        return new ObjectResult(_localizer["Hi"]);
    }
}

Result: