Just set the culture/uiculture to the language they select. I'll post example when I'm at my computer

Hi Rocio, as promised, some examples. Currently I set the Thread culture info to the language they have selected, although not sure that is strictly required, but it helps with internal code stuff when you need the culture. You may be able to accomplish the same just with a session variable or a querystring parameter.

At the top of my master template, I check for a session variable (this is set when they select a different language from a dropdown of available languages) and set the Thread culture.

if (Context.Session.Keys.Contains("Culture"))
{
    var cultureString = Context.Session.GetString("Culture").Replace("\"", "");
    Thread.CurrentThread.CurrentCulture = new CultureInfo(cultureString );
    Thread.CurrentThread.CurrentUICulture = new CultureInfo(cultureString );
}

At the bottom of my master template I then call a javascript function, passing it the CurrentUICulture language code SetCulture('@Thread.CurrentThread.CurrentCulture.TwoLetterISOLanguageName');

SetCulture function, checks the language code and sets the correct url

    //switch templates based on the current TwoLetterISOLanguageName
SetCulture = function(lang) {
    //check if using correct url template
    var url = location.href;
    if (/(\/\w{2}\/)/.test(url)) {
        if (lang === "en") {
            location.href = url.replace(/(\/\w{2}\/)/gm, "");
        } else {
            location.href = url.replace(/(\/\w{2}\/)/gm, "/"+ lang + "/");
        }

    } else {
        var newurl = new URL(url);
        var urlstr = "/" + lang + newurl.pathname;
        location.href = urlstr;
    }
}

In my header I have a ViewComponent which displays the various countries and currencies that can be selected, but basically when they select a flag, a javascript function calls a surfacecontroller which sets the culture and session variable to the select language.

    $(document).on('click', '.flag', function (e) {

        ChangeCulture($(this).data("id"));
    });

ChangeCulture = function (lang) { 
    $.ajax({
        url: "/umbraco/surface/clientsurface/changecurrentculture",
        type: "GET",
        dataType: "html",
        async: true,
        data: {"language":lang }
        , success: function (data) {
            if (data) {
                SetCulture(lang);
                $("#drp_currency").val(data);
            } else {
                console.log('error: no data returned');
            }
        }, error: function (xhr) {
            console.log('Error: ', xhr.status + ' (' + xhr.statusText + ')');
        }
    });
    return "";
}    
    }

SurfaceCntroller method

    public JsonResult ChangeCurrentCulture(string language)
    {
        if (language == "en-GB")
        {
            language = "en";
        }
        var newCulture = new CultureInfo(language, false);
        _httpContext.HttpContext.Session.SetString("Culture",JsonConvert.SerializeObject(newCulture));

        return Json("success");
    }

Hope this helps.

is working on a reply...