language packs in appliactions

hi guys and gals, its been a while since ive actually posted a question here (since im just so uber l33t jk) anyway, im developing an appliaction that i want to be multi-lingual, i know of a few methods of how to achive this (defining variables, constants, and arrays) but i would like to get a general opion on what other people would do,

the method im concidering at the moment is to use an array, for example

$lang = array();

$lang['welcome_note'] = "Welcome to my app.....";
$lang['note'] = "all your base are belong to us";
....


so you get the idea, the only thing im thinking of is that it may slow the appliaction down a fair bit.

Any thoughts?