I managed to add extra languages for HW keyboard with the first Xperia that jolla supported, and one of them was greek too. Not sure if I still have a howto. I found some files-languages for the fingerterm keyboard I made many years ago. I asked that back on together.jolla.com:
If I remember correctly it worked quite good, but not close good as on pc: not easy to change language and maybe the punctuation was missing ? That was ~8 years ago.
Also, some sailfishOS versions latter not sure it it will work. If I make any tests I’ll let you know
@ApB I just added Greek support for hardware keyboard, tested it, working without punctuation. At least worked on xperia 10 iii , sockingly simple, I edited this file:
Saved, closed settings completely and then opened it again, went to Settings → System → Text input → Hardware keyboards and it was third from the end. Control + Space works to change the language. It seems to work on android apps too.
I suggest backup the file before any changes. Let us know if it worked for you.