How to detect non-latin letters?

 //char can be casted to int to acquire letter's code
 //returns true if letters are latin
 bool CheckForNotLatin(string stringToCheck)
 {
     bool boolToReturn = false;
     foreach (char c in stringToCheck)
     {
         int code = (int)c;
         // for lower and upper cases respectively
         if ((code > 96 && code < 123) || (code > 64 && code < 91))
             boolToReturn = true;
         // visit http://www.dotnetperls.com/ascii-table for more codes
     }
     return boolToReturn;
 }