As this is a persistent issue, I want to leave as an ending comment what worked for me as of today, which is the solution presented in this post:
https://superuser.com/a/1235405 -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/518056 Title: cedilla appears as accented c (ć instead of ç) when typing 'c To manage notifications about this bug go to: https://bugs.launchpad.net/xkeyboard-config/+bug/518056/+subscriptions -- ubuntu-bugs mailing list ubuntu-bugs@lists.ubuntu.com https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
