I created an account on es.wiki - https://es.wikipedia.org/wiki/Usuario:Amire80-beta-auto-enroll-test-2015-01-25-01 .
I went to the beta tab in preferences, checked "auto-enroll" and saved.
I saw VisualEditor and VisualEditor language tool immediately enabled. The rest of the beta features were not.
When I tried going to Special:ContentTranslation, it didn't work, because it can only work if the beta feature is enabled.
@MarkTraceur told me that if auto-enroll is enabled, the beta feature is supposed to be enabled as soon as it's checked, but this doesn't seem to happen.
I am not sure whether it's an issue in the BetaFeatures extension itself or in the way that ContentTranslation uses it.
You can find the relevant ContentTranslation code here:
* https://git.wikimedia.org/blob/mediawiki%2Fextensions%2FContentTranslation/333c416b1f0007adb29d1a09885809b23d58c016/ContentTranslation.hooks.php
* https://git.wikimedia.org/blob/mediawiki%2Fextensions%2FContentTranslation/333c416b1f0007adb29d1a09885809b23d58c016/specials%2FSpecialContentTranslation.php