I don't miss karma being a thing (and people focusing on growing it by pleasing as many as possible, instead of focusing on content) but I'm also past the age of getting good/bad grades for doing my homework or for participating in class ;)
I'm pretty sure introducing karma will boost low effort reddit-like posts. And those don't need any encouragement, imho.
In French, it would be better to use "Achetez" (third person plural, considerate the polite form) instead of the much more informal "Achète".
Also, I would suggest to make circle of stars broader, broad enough to include the slogan in its entirety. There is room left around each flag for that, and fr the few ones where it won't be enough (like the last one) it won't be enough, it should be ok to make the font a tad smaller/play with spacing on that one flag.
Edit: clarification.