https://www.cbr.com/scarlet-witch-accent-avengers-infinity-war/
Why Scarlet Witch Lost Her Accent For Avengers: Infinity War
Appearing on Josh Horowitzs Happy Sad Confused podcast, Infinity War directors Joe and Anthony Russo cleared up the mystery, explaining that Elizabeth Olsens Wanda Maximoff had barely a trace of her accent due to the events of Captain America: Civil War.
We have intentionally tried to strip that accent away for a couple of reasons.
one of the most distinguishing characteristics that [Wanda] has is her accent, Joe Russo said. So if youre gonna try to disguise yourself or hide yourself or not be caught, youre going to try to limit those trigger warnings that would make it easy for someone to identify you, which would be inclusive of her accent
For us, it was very intentional that we would just keep stripping that accent down to show her acclimating and hiding.
Considering Scarlet Witchs abilities, it doesnt necessarily hold up that changing her accent is going to do much to keep attention away from herself, especially when she hasnt altered her appearance. Another reason fans may be skeptical of the Russo brothers explanation is that, in Infinity War, shes primarily seen in private conversation with Vision (Paul Bettany), where she would be free to speak with her accent or in her primary language.