Hello Xavier,

Thank you for posting in our community.

I am currently investigating how locale can be set in cases that is not in the locale list of the igLoader control. I will keep ypu poste don my progress and I will get back to you until the end of the business day tomorrow,  September 16th,  with my findings.

Please feel free to let me know if you have any additional questions regarding this matter.

For accomplishing a locale based on the current browser language and reverting the locale to English when current language is not supported the UserLanguages can be used.It can be retrieved from the Request and later set as the locale option for the igLoader. By design 'en-US' locale is built in the Infragistics controls and there is no need to explicitly set it if this is the current browser language. If the language is different form English it can be retrieved and used for setting locale option afterwards when the igLoader is created. All localization files are in the i18 folder. For example:

 @{
  var userLanguages = Request.UserLanguages;
  string currentUserLang = userLanguages[0];
  if (currentUserLang == "en-US" || currentUserLang == "en")
  {
   currentUserLang = "";
  }
  //TODO check if currentUserLang is valid (exists in i18n dir)
  
    string path = "Your current path of the i18 folder";
   //get all the js files names in the i18 dir in array of strings
    string[]    files = Directory.GetFiles(path, "*.js");
   //loop trough this array and check whether the browser language matched any of the supported languages.
   for (int i = 0; i < files.Length; i++){
    if(currentUserLang == files[i].Substring(70,72))
    {
        currentUserLang = userLanguages[0];
    }
     //if currentUserLang does not match any of the supported languages set it as an empty string which will imply English localization
    else{
     currentUserLang = "";
    }
  }
  }
  @(Html.Infragistics()
        .Loader()
        .ScriptPath(Url.Content("http://localhost/ig_ui16.1rel/js/"))
        .CssPath(Url.Content("http://localhost/ig_ui16.1rel/css/"))
         .Locale(currentUserLang)
        .Resources("igGrid.*,igCombo")
        .Render()
    )

Please let me know if you need any further assistance with this matter.