Paid Membership Translation

Q. How can I localize it? Where can i find the language file?

A. Paid membership manager language files are
en-GB.com_simsu.ini in  /language/en-GB/ folder

and two files
en-GB.com_simsu.ini
en-GB.com_simsu.sys.ini
in /administrator/language/en-GB/    folder.

You need to change their name and copy these files to your language folder. For example, to translate into french, you need to copy those files
fr-FR.com_simsu.ini      to /language/fr-FR/      folder
and
fr-FR.com_simsu.ini
fr-FR.com_simsu.sys.ini
to /administrator/language/fr-FR/    folder.

Q. How can I customize the layout/css?

A. You can modify these files:

/components/com_simsu/views/plans/tmpl/default.php