yep, I'm also wondering this and yep I was doing echo $currentlang and it looks like that echo $currentlang cannot printout anything or the variable is empty.
I was notifying that when was peaking page source via web browser php commands are partly printout to source code which in my understanding is not supposed to be happening.
in example this footer if statements looks following via browser view source code option. So I'm little bit confused why php code is visible, where it supposed to be run on server side and send ready coded page to user browser.
'<?php = pll_current_language();
if(=="fi"):?>
<?php echo ; ?> <p>Code for language 'fi'</p>
<?php elseif(=="en"):?>
<?php echo ; ?> <p>Code for language 'en'</p>
<?php endif; ?>'