Please note that we already gave you link to page about this issue and information that we are aware about other flags solutions possibility and consider it already. Thanks that you want to show us how important you think it is 
Also please note that Google doesn't have to open any javascript and see all flags which are in drop down menu. The code which you gave is for browsers and it changes drop down menu to make it visible for users. All bots see it immediately because drop down menu is included in HTML output (not taken by Ajax) - just please find in your HTML output this:
Code:
<div class="vbmenu_popup" id="vbettranslations_menu" style="display:none;margin-top:3px" align="left">
And you will see that drop down is included in HTML output and robots see all the flags, just browsers doesn't show it at the begging because of style display:none and script which you pointed is only for browsers to make it visible.
I checked your page in web analyzer which you gave and the results are drastically different that which you gave here.
HTML load: 0.46 second
Total images load: 3.51 second (including all images not only flags).
And please note once again that you are interpreting results in wrong way, because you miss the concept of web browsers cache. Web browsers are caching images and do not ask for those in next requests. So time added by flags download is minimal for your users which are watching hundreds of your pages and took flags at the beginning. I already point your attention on this and you can check it yourself just going to your own forum and seeing that you are not waiting seconds for any image but have it immediately.
Still we are aware that our users would like to have also other option for flags and we will test solution proposed in thread which I pointed you before.