Hi Niko,
The link was a starter in creating a language selector. It’s not the exact solution to your problem. Sorry I didn’t make this clear in my previous comment.
Are you comfortable with coding? If you are, you can use hampusborgos/country-flags: SVG and PNG renders of all countries’ flags. (github.com) as your source of SVGs/PNGs to use. Then with the use of CSS Flex + a parent container, you should be able to add country flags to your language selector.
If you’re not comfortable with coding, your best route is to hire a developer to do this for you.