OK - I don't know the exact structure of artisteer themes as its a commercial paid for product that I don't have, but I'm assuming they will follow the common code in most themes.
Add the two flag images you want into the them pix folder, then, in the layout file for the page you want the flags on (frontpage.php, for example - this example is from general.php in anomaly) add the code highlighted below:
<a href="#"><img src="<?php echo $OUTPUT->pix_url('yourflag1image', 'theme'); ?>" alt="Language1" /></a>
<a href="#"><img src="<?php echo $OUTPUT->pix_url('uyourflag2image', 'theme'); ?>" alt="Language2" /></a> </div>
<?php echo $OUTPUT->lang_menu();
The div flags has been added in case you then need to add any css to your style css files to position the flags just how you want them (You can use css to size them as well, but I would recommend getting the size right in the first place when you save the images, then you wont need to do that). Edit the links and the image names/alt text appropriately and you should be done.