Make it easier to try out the translation process without (yet) creating an account

### Describe the problem

As we all know, creating an account is a big showstopper for users, which is 9000% more true when they don't know what they're making it for. So it would be cool if we were more easy on people who don't (yet) want to create an account.

### Describe the solution you'd like

* On the `/engage` page, at least move the "Register" button towards the end. Or remove it, to remind the user down the line that it's best for them to register.
* Don't say straight up on the `/engage` page that they need to register.
* On the `/translate` page it should be more clear why the "save" button is disabled. I think the `title` attribute doesn't quite cut it. Perhaps add a tooltip?
Or make the button not disabled and create modal saying that you can either add a suggestion or register to save it. Say that they can register later, and of course don't show the modal again. A modal may be too unnecessarily intrusive though.
* Also #7715.

### Describe alternatives you've considered

_No response_

### Screenshots

_No response_

### Additional context

Related: #7715