UX/design team, what do you think?
It would obviously need to only show when experimental features are on.

In my opinion it was a mistake to implement this function into the core from the beginning. Would have been very much suited a great extension (whether bundled by default is another question), and consequently showing up in this UI space.

Now we need to show the button in the Notebookbars, so I agree with the request. Experimental features need to be a large button, maybe next to Review > Spelling, or placed at the end to deal with the inflexible layout. Or put into the context menu.

John, what do you think?

My personal opinion is that we should have parity. If a user switches between both UI options then it is a regression if not available in the tabbed UI. Additionally there is documentation available that targets both interfaces. The location for the command can be debated but it should exist. In Microsoft Office the equivalent feature is under the Review Tab in the language subsection. I would suggest putting it next the the Spelling section, to the left hand of the Comment icon.

So let's do it.

The command is uno:Translate, to be added to sw/uiconfig/swriter/ui/notebookbar.ui, after and similar to <child>... id="Review-SpellingAndGrammarDialog">