function $lang->sprintf()

[Steeep]

I need to take the $ lang->sprintf(), but not how.
The full code that I have ..

<setvar glastuser>get_user($stats['lastuid'])</setvar>
<setvar fn_lastuser>format_name($tplvars['glastuser']['username'], $tplvars['glastuser']['usergroup'], $tplvars['glastuser']['displaygroup'])</setvar>
<setvar lastuser>build_profile_link($tplvars['fn_lastuser'], $tplvars['glastuser']['uid'])</setvar>

<setvar lastuserl>$lang->sprintf($lang->stats_newestuser, $tplvars['lastuser'])</setvar>

As I can do? Thanks in advance.