Just to add to your solution, I did the following to also display the words "is" or "are" depending on whether there is 1 or more items in the cart. Doesn't affect the tool tip either.
Code:
{if $minicart_total_items > 1}
<td>There are {$minicart_total_items} {$lng.lbl_item}s{$total} in your cart</td>
{else}
<td>There is {$minicart_total_items} {$lng.lbl_item}{$total} in your cart</td>
{/if}