Created attachment 243328 [details]
Contains all files mentioned in my description that will help you reproduce and identify the problem

Hello,

In gedit's open file dialog box, there is an option for choosing the character encoding. The default option is "Automatically Detected" which I am afraid it doesn't always work.

I am attaching a file (gr.srt) with encoding (Greek) ISO-8859-7. I verified its encoding using the chardet utility in the terminal and I am also attaching chardet.png that shows exactly this. If you open this file (gr.srt) with gedit and encoding auto detection and you leave your mouse over the respective file's tab, a hint will appear reporting the Western ISO-8859-15 as the detected encoding. Of course as a result, the file's content is unreadable. (Attached geditWrong.png)

If you open the same file by choosing (Greek) ISO-8859-7 in the open file dialog box, the respective hint properly shows the correct encoding and the file is readable. (Attached geditCorrect.png).

Bear in mind that once you have opened the file with ISO-8859-7, it will always open correctly even if you choose "Automatically Detected". It seems that gedit remembers your option and doesn't actually try to detect the actual encoding. In order to reset to the initial problematic behavior, you have to manually select (Western) ISO-8859-15 once. It seems to me that it is very probable that this is another issue but yet related and it will also help you to not get confused in your tests.

Finally, I would like to grab this opportunity and ask you to add an encoding choice in gedit's menu because in the open file dialog, it is quite "hidden" in the sense that most people open files by double clicking them. I even found this option on the net, it didn't even cross my mind that such an option would be available there. Also, I have found quite many frustration reports on the Internet from people who use non Latin alphabets, I have even found a bug report in Ubuntu that was closed because the reporter unfortunately failed to provide the required evidence and instructions.

Thank you very much.

P.S
Since I am only allowed to attach one file, note that all files I have mentioned above are included in geditEncoding.tar.gz