IMHO the most important and enduring language will be the one embedded natively inside your database of choice. SQL and it's many add-ons and extensions are the core foundation of an ERP system (which over it's lifetime will probably be interfacing with different external clients written in several other front-end languages). Model your business rules tight in the tables with triggers and stored procedures handling the standards like cascading updates and deletes, and all the non-standard data transformations handled by your database code, enforcing the business rules of your Enterprise at the core. SQLServer, PostGre, MySQL, SQLite all are good options