I did some research over this issue and realized that everyone was suggesting to use iconv or recode to change the encoding of the file to UTF-8. The thing is that I do not want to change the encoding of the file. I just want to use gedit in order to edit the file (my file's encoding is iso-8859-7) and save it using the same original encoding. Is there a way to do that?

I know for a fact that Kate has a menu option that lets you determine the encoding of the file. Even the default text editor of Windows (!!!!!!!!!!), notepad, allows you to select the encoding. I mean, I like having an extensible default text editor and all, but there are some features that are not optional.