If you want to use multi language support for your custom fields, just name them {CUSTOM_FIELD_1} / {CUSTOM_FIELD_2} / {CUSTOM_FIELD_3} / {CUSTOM_FIELD_4} and add/edit the language strings in plugins/mcf/codebase.php. At least upload & install the plugin as described in the docs.
Thanks for this plugin works like a dream. ;)