You should have just asked in the other thread. Yes you can install a version for GB over the EN_US version. However instaling a 64 bit version if you have been using a 32bit version will cause issues in most cases.

See https://thunderbirdtweaks.blogspot.com/2019/09/i-lost-my-profilemail-on-update-to.html

This is still being discussed in bug 1542025 and I am trying to get my head around exactly what it all means.

It's apparently a 32-bit version, which was what was originally downloaded automatically on clicking 'download'. I have a new W10 laptop with plenty of RAM/CPU etc. Will TB run better in a 64-bit version? I don't use the calendar or any other add-ons (though I really miss the Manually Arrange Folders add-on which seems currently unavailable)

I have looked at the different versions on offer - can you tell me what the difference is between Windows 64-bit and Windows MSI 64-bit? Should I go with the 32-bit British English version? Or uninstall what I have and reinstall the 64-bit one? I do not understand much if anything in either of your two references. I seem to have two default profiles - one is plain default (doesn't seem to be in use) and the other is default-release. I would worry about transferring all my data to a new installation.

Sorry to be dim!

At this point in time just go with the 32 bit version. don't touch the MSI version, I used it once and all the options dialogs did not appear. It might be good for companies installing for lots of staff, but I don't think it is meant for the rest of us.

OK, thank you very much indeed. I'll do it over the weekend when things are a bit quieter!

best wishes Kate