Forgive my ignornance, but I thought in the West 88591 is the standard to open any file?
No.
The process in Geany (IIRC, didn't refresh my memory, but its roughly right) is:
1. if the encoding is forced (the setting in "more options" in the open dialog), use that and succeed or fail, don't try anything else 2. check for BOMs and use that (if UTF-8 just validate, don't convert) 3. try the default from the setting you show above, ie UTF-8 and validate 4. look for encoding message in file (some common things like HTML `charset=`, or editor `coding: `), try that 5. try every encoding in the list in some order, first with no error wins
Something about the file makes it fail when trying encodings, but it does succeed when forced (for me). It may be something in the exact way the Glib convert is called in the various cases.