Hi Chanettk, thanks for the great question.
I will look into this for you, although I'm not quite confident at this point as to how I could do this. It would likely be done by adding a background image to each drop-down language through CSS, but anything more complicated would mean trying to change the Google functionality itself, which I'm not sure could be done.
This would obviously be a great addition though, and like it! I will see what I can do, although I do not know if it will be soon that you see results in the plugin.
If I find an answer I will let you know right away, then at that point I will try and make the time to add this in the next update.