This issue is very common if you're using a language with special characters. I'm a norwegian myself and we have some special ones, I know this issue well. The thing is that the default character set of Fedora is the modern UTF-8. The beauty of UTF-8 is that everyone can see all kinds of characters. Because of this, we should encourage the use of UTF-8, as it will help to lower the gap between all the computer users of the world. Having one character set is much better than having many.
Most users however, use windows. The default in windows is the ancient ISO8859-something. The ISO8859 character set only shows some of the worlds special characters, because of this we have a lot of different ISO8859, in europe we use ISO8859-1 or ISO8859-15 (which has the new Euro character). And sadly, we all have to deal with windows users from time to time.
So what happens when you send UTF-8 characters and the people using ISO8859-1 reads it? Well, it's shown as an obscurated character.
Luckily, Xchat has a way of solving this. You can enter the server list, which is found under "X-Chat", select your network and enter "edit mode" (the checkbox). In edit mode, select the character set from the list, since you're in spain, choose ISO8859-15.