Not an answer to your question but I, a European, did that in reverse on one occasion. Was on student exchange in Japan with people from a variety of countries. Another student was asking around for international coins to take home as a souvenir. I kept forgetting to bring her a euro so in the end I told her she should ask the Argentinian instead - because I had her saved in my head under “Spanish”. I cringe every time I think about that brainfart.

Sooo… in a way this IS an answer: perpetual brainfarts.