In multi-language countries, e.g. Belgium or Switzerland, can one side tell whether you’re a citizen from the other side or a foreigner from a neighbouring country? Can Flemish people tell Walloons apart from the French? Can Swiss Germans tell Italians apart from Swiss Italians?

I have heard stories that Swiss Germans don't like Germans very much, and Swiss French don't like French, etc. But if you are from a country that speaks a national language fluently (like French) but just happens to be in a mismatched canton or region (German canton) do you just slip under the radar because they think you're just from a different part of the country?