You can find one localization example in download package, file name is "phphtmledit\localization.php", you can find the following code in this file:
<input type="radio" name="RadioList" <?php echo Checked("nl-nl", $CustomCulture) ;?> value="nl-nl" onclick="jumpTo(this)"/>
the dutch language resource file is "cuteeditor_files\Languages\nl-nl.xml", the english resource file is "cuteeditor_files\Languages\en_en.xml", you can copy those string which are not translated to dutch from "en_en.xml" to "nl_nl.xml", and then translate to dutch. After you finish this step, test it again.
Regards,
Eric