Authors temporarily forget that their setting is supposed to be foreign
A work that sometimes slips into the habits, moral values, or language quirks of the writer's native culture, even though it takes place in an existing foreign culture, or in a made-up, but explicitly foreign-themed setting. Compare to Like Reality Unless Noted, that is an omnipresent trope, but this trope is caused by the the same thinking, applied to the entire world. Though strictly speaking, this is not a Did Not Do The Research trope, after all, it's the writer's choice to mix the cultures in his own fictional setting however he wants to, it can still create a dissonant feeling for outside viewers, especially foreigners, who still see the culture as something "special" instead of generic. Related to Ooh, Me Accent's Slipping when actors do this, and Anachronism Stew when it's an older culture that shows signs of a newer one. In fact, accusations of Anachronism Stew in a Hollywood historical film, are often this trope at the same time, from a different perspective: For example if Ghengis Khan says a blatant americanism, the american audiences will likely see it as a perfectly "generic" saying, and only citicize the fact that it didn't exist back then, while the mongolian audience would be more concerned about Ghengis Khan talking like an american, than about the age of the saying.