The "official" Beta Testing program is no longer active. There are various individuals who have volunteered to translate the help and error messages who also have bee instrumental in finding errors.
What is a Beta release of software?
A software release is the distribution of software code, documentation, and support materials. The software release life cycle is typically composed of discrete phases that describe the software’s maturity as it advances from planning and development to release and support phases. It generally begins when the features of the software are complete. The focus of beta testing is on reducing impacts to users, often incorporating usability testing.
The process of delivering a beta version to the users is called beta release. This is typically the first time that the software is made available outside of the organization that developed it.
The users of a beta version are called beta testers. Typically they are customers of the organization that develops the software, willing to test it at no charge.