The editor does not switch static localization strings when the language is changed by clicking the flag on language selector. The problematic place is on the line number 793 in file EditorProvider.vb:
 
Dim path As String = HttpContext.Current.Server.MapPath(_localeFile.ToLower.Replace(".resx", Locale & ".resx"))
 
Please remove leading dot from the first string parameter:
 
Dim path As String = HttpContext.Current.Server.MapPath(_localeFile.ToLower.Replace("resx", Locale & ".resx"))
 
This correction allows the intended functionality of function IsLocaleAvailable(). Thanks.
 
Correction:
Sorry, the solution published about is wrong. It doesn’t work for default language. However, this issue still exists in dnn version 6.0.1. Here is what works for me (C#, dnn version 6.0.1):
 

    private bool IsLocaleAvailable(string Locale)
    {
        string localeExt = String.Empty;
        if (Locale.ToLower() != "en-us")
        {
            localeExt = "." + Locale;
        }

 

        string path = HttpContext.Current.Server.MapPath(_localeFile.ToLower().Replace(".resx", localeExt + ".resx"));
        if (File.Exists(path))
        {
            return true;
        }

 

        return false;
    }