Selection to lower case - a PageSpinner AppleScript ツゥ Jerry テ⒃an, Optima System 1997.
You can add characters to upperTable and a matching entry in the same position in lowerTable to localize it to handle language specific characters. This script handles e.g., the special swedish characters テ テテ. The script is probably not compatible with languages such as Japanese, that uses 2-bytes ASCII.