Once you install the beta release, open BSplayer and press F1, there you can read the release number (actual beta v2.35.984B dated 17 February, the previous one was v2.35.983B)
Plus before you download it, near the name is a date_time release stamp
Plus you get the new beta notification by e-mail (I don't know if you have to subscribe to receive the notification)
If you mean "How can I know which beta is the last one before the final version is released, so I can download and update only the last one beta and not the before last ones?"............. I don't know, just don't download a beta as soon as it got released but wait 4-5 days, the final should get released after a week of betatest, so if a new beta is not released in the meantime you can send the updated translation, and in the worst case a new beta will appear the next day, but with only a couple of new strings to got translated and if you can't afford another download just ignore it until the final is out
