So, I have checked this, and I am
sure it is working with default miniBB installaton latest release 2.0 RC4b. You can see an example on our forthcoming test demo version:
http://minibb.org/index.php?action=userinfo&user=1"Real name" is the field under "user_custom1" in database.
I have just added in user_dataform.html:
<tr>
<td class=caption4 align=right valign=top>Real name</td>
<td class=caption5><input type=text name=user_custom1 maxlength=15 size=20 value="{$user_custom1}" class=textForm style="width:200px;"></td>
</tr>
and put
$l_usrInfo[12]='Real name';in lang/eng.php that's all. And it's working.
So the problem is somewhere on your side, sorry.