Hello,
The lang Url parameter is a special query parameter. Its presence in the Url indicates that Kentico
CMS should change the current culure if the current culture is different from the value specified in the lang parameter.
The Url with this parameter needs to be created manually. You can use the following method to add the lang parameter to a particular Url
string url = URLHelper.AddParameterToUrl(currentUrl, "lang", cultureCode);To check / change the current culture using API you can use the following property:
CMS.CMSHelper.CMSContext.CurrentUser.PreferredCultureCode.
Best regards,
Michal Legen