hmmm, The arcade who list works for me, maybe you should look on the mod site and parse the mod, compare it to your who.english.php file
Wow. Ever since this issue started occuring, I can NOW see Arcade games being played, but when someone is viewing who's online themselves, it says unknown and when they are viewing the forum it says unknown too. It's all backwards now! lol
Compare your who.english.php to a clean one from the SMF package installer, your missing a line if it says unknown actions when people are viewing whos online.
If its missing from the languages, which I suspect it is, the line should be
$txt['whoall_who'] = 'Viewing <a href="' . $scripturl . '?action=who">Who\'s Online</a>.';
If its not missing, then try clearing your cache, however, I would strongly suggest starting a new topic, as we have pretty much high-jacked this one lol