The database platform is PostgreSQL. The entire system is written in Python. Database records, including those specifying the User Interface, are loaded via XML files.

So I would suggest:

• Python
• XML
• ISO/ANSI SQL

I would STRONGLY suggest attending OpenERP Functional and Technical training offered either by OpenERP or by a certified training partner.

You won't be able to learn as much in an organized fashion on your own. In my opinion, the 70 hours of training you get would take you AT LEAST 350 hours to 700 hours to learn 'on your own'.

You need to review A LOT of material if you want to do this on your own.

Start with https://accounts.openerp.com/forum/Help-1/question/6817