While trying to reproduce the supposed bug, I found out that my office software was the one at fault here.
Manually editing the csv file with vim instead of LibreOffice fixed the problem.
Anyway if you want to take a look, here is a completely normal and working workflow implying accents and spreadsheets (spreadsheet url is included in http request node and at the end of this post):
I just tested with n8n. Started with your workflow. Then transformed it back to CSV, saved it and then opened with Libre Office. That file looks then great in Libre Office. But if I just download the file with my browser and open it then I have the same problem you have. Seems like it uses different character-encoding. If I manually change it in the Libre Office Import Dialog from “UTF-8” to “Latin 3(ISO-8859-3)” everything gets displayed correctly again.