For context, this is a small group of freedom fighters from different parts of the world, roaming around Nazis occupied France, performing (unsanctioned as they are all technically civilians) hit and run attacks on Nazis. Some of them aren't even European, either in terms of nationality or of ethnic descent.
And while I'm pretty sure I've avoided any cultural stereotypes about any of their ethnic groups or nationality, I've also avoided putting in anything into their dialogues to show their accents. But I have had another character (their prisoner who is the main POV character) try to wonder where they are from given their accents which he's not familiar with. Even the narrative is deliberately being vague as no mention is made of where they are from.
The thing that struck me here is just how much of a characters culture (including accent) do you actual need to show for readers to realise where they are from, and how do you make sure your not being offensive by including any such details? For example, does altering their dialogue to show the fact they are not speaking their native tongue mean your are being racist by default? Or is that just an issue with a person who might just see any acknowledgement of that persons heritage/culture/etc as being such?