Mispronouncing everything. It's more a problem of "I don't want to make them feel stupid" because mispronouncing stuff is often seen as a failing on the reader's part even though it's not their fault for assuming the letters make the usual sounds, but there are a lot.
Petrichor: in French "ch" makes a "sh" sound so people who don't know it's a Greek root word pronounce it "petrishore" instead of "petrikor"
Khay/Khaled: they're qatari, and in arabic kh is a kind of rolled guttural "R" sound, so their name is pronounced Rei/Raled. But people know Khaleds in real life that pronounce it Kaled so assume (naturally) that the characters name is Kay.
Aide: pronounced like the letters A-D like Persephone isn't pronounced like telephone. This one's actually going to be explicit in the plot, but also French doesn't have the "pronounced e" at the end of names at all so they have no way of knowing.
Sarin: pronounced the English way with the "-in" being like "inside". To make that sound in French it would need to be spelt "Sarine" but I didn't change the spelling, so people often pronounce it "Saruhn".
So far when talking in person with people who buy the comic they've sort of picked it up intuitively when talking about the characters but I don't want them to feel bad for getting it wrong.
Anyway, here's the comic if you want to read, the hardcover French version'll be available on my website soon!