The only other plugin active was Advanced Custom Fields which hadn't been setup at all, nothing was defined for it. I tried disabling it but nothing changed.
To setup the menus I went to Appearance->Menus->Manage Locations and assigned the two menus I had created to each language; english and greek in this case. If I go to "Edit Menus" it lists the assignments properly in the parenthesis next to the menu name in the dropdown.
Previous to that I had added greek as an extra language without changing any of the settings that polylang suggested for the language (ISO code, locale, etc).
In language settings I have:
- Default language: english
- Detect browser language: disabled
- URL modifications: option 2
- Hide URL language for default language: disabled
- When using static front page, redirect the language page: enabled
- Activate languages and translations for media: enabled
I'll install WP & the plugin later on in a separate new installation and see if it works then with all default settings and compare options. Before I installed polylang I had made some changes to settings (pretty permalinks, etc), but even if I restore those to default currently there is no change. Also ACF was installed before I added polylang.