No, they are speaking English.
As long as they are, asking the question of where their Sokovian accents went is valid.
If they speak Sokovian with an English accent at some point, your question will be right.
That depends if they learned English or if they grew up speaking it. For example, many people treat an Indian accent, Caribbean accents, or accents from African countries as if they are illegitimate accents when the people have grown up as native English speakers. We know that Wanda speaks Sokovian but if she grew up speaking English then her accent is as legitimate as a British or American accent.