Even if the lang changes weren't done, you'd still see it as an option in the ACP if you have uploaded the admin_userlist.php file to the right directory. Double-Check your locations... it should be in the site\admin\ folder. If it IS there and it still isn't showing up, it has to be a problem with your site (likely with the collapsable ACP bars or the EZ Portal mods you mentioned). I have no experience with either of those so you'll have to ask at their threads or forums for help.
I decided against giving you access to my Admin Panel, and didn't feel that phpbb.com would appreciate me posting 15 screenshots, so I put together this page.
The forum that I use that ACP for is on my developemental server is here, and as I had previously stated, I have not noticed any errors or conflicts with Admin Userlist, ezPortal, ezPortal Admin, the DHTML Collaspable ACP Nav Menu, as you can see from the screenshots, it is not a "Vanilla" phpBB 2 Admin Panel.
Have you eXtreme Styles MOD? DHTML Collaspable ACP Nav Menu have problems with it. Maybe here is the source of the problem. In my board Admin Userlist works many time without problems but I uninstalled DHTML Collaspable ACP Nav Menu.
This is the first mod I ever installed, and just want to say that it seems to work great and was not too hard for me to figure out (had no clue how to do a mod 24 hours ago).
I'm using it on a new installation of phpBB 2.0.23, and I installed it in the subBlack template (all six color variations), as well as in subSilver.
I had been using a similar mod for about a year which came pre-installed with a free-hosted forum, and I was looking to duplicate all of the same mods after I moved to a paid host.
I was really glad to find this here. Thanks.