Hello Natalia,
you can create a template yourself as html-file, where you can set the code-page. You then just have to point to it in your notification task. If you look in the templates-folder, you should see other mail-templates as html-files (for the assignment-requests), so you could use those as a base for your custom templates. 
You set the path to the template here in the attribute "MESSAGEFILE".
Maybe the easiest would be, to just keep the names of the files (because they are found throught the Notification Operation) and just turn them into HTML-files, so you just have to change the "tpl" here into "html".
Regards,
Steffi.