Any ideas on what I need to do to fix this? Would an upgrade to 2.3.1 fix the problem? Given this problem arose from a version upgrade, I am a little reluctant to jump in and do an upgrade without knowing it will be ok
V2.3.0 RC3 is oooold, why not upgrade to a recent version? Stable is 2.3.1, and 2.3.2 RC1 is out too.
If you look around in this forum just a little you might notice that translatable is broken in 2.3.0 and 2.3.1, causing the problems you see.
Good news is that SS 2.3.2 has it fixed,and improved, so upgrade to that, and it should work again. However the translatable concept has changed, so it will not be an easy and automatic upgrade, you might have to manually transfer the translated pages.
Further progress. After finally completing the upgrade (For future reference, don't get distracted in the middle so you don't forget some folders etc) I no longer get errors when I try to change languages but they still don't work.
However I am unable to log in to admin. Am now heading off to look for ideas on forums to solve this logging in problem.