Viewing a history listing
Somehow, summary and Save, Preview, Show Changes buttons are wrongly enumerated (or omitted from tab enumeration) when editing messages or templates. So it's not possible to switch from editor to summary with Tab key. Problems happens today. I use monobook.
I have no idea what you mean. I think a screenshot would mean the world.
Start editing. Then press tab key. Focus and cursor should be moved into Summary field. Work in case of LiqudThreads. In regular edit window focus came to Cancel, Help and special symbols area.
If you don't mean the translation dialog from Translate extension, this is a bug in MediaWiki and should be reported on the bugzilla.