[HELP] img with onclick event in popup prompt? HTML + JS

Hello sir/madam,
I was working on my website http://nxtgc.ddns.net/thomascv.html and I thought adding a button where you could change the language. I thought of having multiple text boxes with the same text in different languages and ids so when you would press a flag the the corresponding language would show and the other language would dissapear. I also thought of adding multiple websites for the languages and so on. I somehow came to this conslusion to add a popup prompt to show when the page is loaded and it would implement the svg flags from wikipedia with the event to change the corresponding lang to visible. But somehow I just cannot manage to figure out how I should do it and why my code doesn’t work.