use_htmltrans=0 do not work at rss

I write in Spanish, as you can see at:
https://www.pilas.net/
I obtain the proper character display setting use_htmltrans = 0 as recommend https://www.ads-software.com/support/3/1569
However the RSS syndication do not show the proper characters, see:
https://www.pilas.net/wp-rss2.php
where you can see the last post as:
??Podr?? llegar a desaparecer la PC?
instead of:
?Podrá llegar a desaparecer la PC?
I have set rss_language=es and I use WP – March 10 daily snapshot.
Can you give me some tip?
Tks! Rodolfo