Thanks for your advice, Tal, I think it's definitely
$minicart_total_items
but I don't think I can put the Smarty tags into the language variable, as explained above, so I will somehow have to put the code in the language variable, into minicart_total.tpl, which uses this code:
Code:
{$lng.lbl_cart_X_items_total|substitute:x:$minicart_total_items:total:$total}