I know this is a very old question, but having just had to solve the complete set of related issues, I thought I would share my solution.
Below is a complete solution, including a few extra tricks to allow easy changing of language. It allows for specific cultures, not just specific languages (but only the language part is retained in this example).
Features include:
- Fallback to browser locale in determining language
- Uses cookies to retain language across visits
- Override language with url
- Supports changing language via link (e.g. simple menu options)
Step 1: Modify RegisterRoutes in RouteConfig
This new routing includes a constraint (as others also suggest) to ensure the language route does not grab certain standard paths. There is no need for a default language value as that is all handled by the LocalisationAttribute (see step 2).
public static void RegisterRoutes(RouteCollection routes)
{
...
// Special localisation route mapping - expects specific language/culture code as first param
routes.MapRoute(
name: "Localisation",
url: "{lang}/{controller}/{action}/{id}",
defaults: new { controller = "Home", action = "Index", id = UrlParameter.Optional },
constraints: new { lang = @"[a-z]{2}|[a-z]{2}-[a-zA-Z]{2}" }
);
// Default routing
routes.MapRoute(
name: "Default",
url: "{controller}/{action}/{id}",
defaults: new { controller = "Home", action = "Index", id = UrlParameter.Optional }
);
}
Step 2: Create a Localisation attribute
This will look at controller requests, before they are handled, and change the current culture based on the URL, a cookie, or the default browser culture.
// Based on: http://geekswithblogs.net/shaunxu/archive/2010/05/06/localization-in-asp.net-mvc-ndash-3-days-investigation-1-day.aspx
public class LocalisationAttribute : ActionFilterAttribute
{
public const string LangParam = "lang";
public const string CookieName = "mydomain.CurrentUICulture";
// List of allowed languages in this app (to speed up check)
private const string Cultures = "en-GB en-US de-DE fr-FR es-ES ro-RO ";
public override void OnActionExecuting(ActionExecutingContext filterContext)
{
// Try getting culture from URL first
var culture = (string)filterContext.RouteData.Values[LangParam];
// If not provided, or the culture does not match the list of known cultures, try cookie or browser setting
if (string.IsNullOrEmpty(culture) || !Cultures.Contains(culture))
{
// load the culture info from the cookie
var cookie = filterContext.HttpContext.Request.Cookies[CookieName];
var langHeader = string.Empty;
if (cookie != null)
{
// set the culture by the cookie content
culture = cookie.Value;
}
else
{
// set the culture by the location if not specified - default to English for bots
culture = filterContext.HttpContext.Request.UserLanguages == null ? "en-EN" : filterContext.HttpContext.Request.UserLanguages[0];
}
// set the lang value into route data
filterContext.RouteData.Values[LangParam] = langHeader;
}
// Keep the part up to the "-" as the primary language
var language = culture.Split(new char[] { '-' }, StringSplitOptions.RemoveEmptyEntries)[0];
filterContext.RouteData.Values[LangParam] = language;
// Set the language - ignore specific culture for now
Thread.CurrentThread.CurrentUICulture = CultureInfo.CreateSpecificCulture(language);
// save the locale into cookie (full locale)
HttpCookie _cookie = new HttpCookie(CookieName, culture);
_cookie.Expires = DateTime.Now.AddYears(1);
filterContext.HttpContext.Response.SetCookie(_cookie);
// Pass on to normal controller processing
base.OnActionExecuting(filterContext);
}
}
Step 3: Apply localisation to all controllers
e.g.
[Localisation] <<< ADD THIS TO ALL CONTROLLERS (OR A BASE CONTROLLER)
public class AccountController : Controller
{
Step 4: To change language (e.g. from a menu)
This is where it got a little tricky and required some workarounds.
Add a ChangeLanguage method to your account controller. This will strip out any existing language code from the "previous path" to allow the new language to take effect.
// Regex to find only the language code part of the URL - language (aa) or locale (aa-AA) syntax
static readonly Regex removeLanguage = new Regex(@"/[a-z]{2}/|/[a-z]{2}-[a-zA-Z]{2}/", RegexOptions.Compiled);
[AllowAnonymous]
public ActionResult ChangeLanguage(string id)
{
if (!string.IsNullOrEmpty(id))
{
// Decode the return URL and remove any language selector from it
id = Server.UrlDecode(id);
id = removeLanguage.Replace(id, @"/");
return Redirect(id);
}
return Redirect(@"/");
}
Step 5: Add language menu links
The menu options consist of a link with the new language specified as a route parameter.
e.g. (Razor example)
<li>@Html.ActionLink("English", "ChangeLanguage", "Account", new { lang = "en", id = HttpUtility.UrlEncode(Request.RawUrl) }, null)</li>
<li>@Html.ActionLink("Spanish", "ChangeLanguage", "Account", new { lang = "es", id = HttpUtility.UrlEncode(Request.RawUrl) }, null)</li>
The return URl is the current page, encoded so that it can become the id parameter of the URL. This means that you need to enable certain escape sequences that are otherwise refused by Razor as a potential security violation.
Note: for non-razor setups you basically want an anchor that has the new language, and the current page relative URL, in a path like:
http://website.com/{language}/account/changelanguage/{existingURL}
where {language} is the new culture code and {existingURL} is a URLencoded version of the current relative page address (so that we will return to the same page, with new language selected).
Step 6: Enable certain "unsafe" characters in URLs
The required encoding of the return URL means that you will need to enable certain escape characters, in the web.config, or the existing URL parameter will cause an error.
In your web.config, find the httpRuntime tag (or add it) in <system.web> and add the following to it (basically remove the % that is in the standard version of this attribute):
requestPathInvalidCharacters="<,>,&,:,\,?"
In your web.config, find the <system.webserver> section and add the following inside it:
<security>
<requestFiltering allowDoubleEscaping="true"/>
</security>
