So many functions!

Hello, There so many functions in php that I can't find the one I need. I have a table like that:

$lang["english"]["category"]    = "Category" ;
$lang["english"]["backpage"]    = "Go to the back page" ;
$lang["english"]["nextpage"]    = "Go to the next page" ;

...

$lang["francais"]["category"]    = "Catégorie" ;
$lang["francais"]["backpage"]    = "Aller à la page précédente" ;
$lang["francais"]["nextpage"]    = "Aller à la page suivante" ;

... And I need to extract "english" and "francais". As it, when I will add another language such as "espanol", it will be automatic... Any idea ? Thanks, Vincent.