A quicky in case anybody has the same issue. I use pine / alpine as a mail client since my firsts steps on the UNIX/Linux world, it always served me well.
Nevertheless, since a couple of weeks, I had this weird behavior where the mail content pager would not display accents (éàü…) while the mail list would! Worse, this inconsistent behavior only happened in tmux.
I suspected something involving locales but no, everything was fine on this side.