The last message states it has been installed and the progress bar is at 100%. Imho it's quite clear.

Of course the bar could be changing colors (should be simple with CSS) - but I wouldn't make that specific for the sample data. Progress bars ideally look the same in the whole CMS.
I also wouldn't hide it. That would be strange and unexpected.

I wouldn't touch the "install" buttons. After a page refresh they would be back at initial state anyway.

Maybe the last message could be a different color or another text to indicate better it's the last one.

Maybe the last message could be a different color (...) to indicate better it's the last one.

+1 for this.

Maybe the last message could be a different color or another text to indicate better it's the last one.

@Bakual should I do these changes

@hardik-codes You don't have to ask for permission. Just do if you're interested 😄

@Bakual What should be the exact change so that it is consistent with the joomla design?

I have no clue - I'm not a designer 😄
Maybe @coolcat-creations has an idea.

If all the steps are bound to each other its enough to have 1 Progressbar, telling the current progress and in the end the result (installation of sample data completed) no need so much messages IMHO.

it is not really. Some steps can succeed while others will not.

Is it ever possible for a scenario like this?
Step 1 - pass
Step 2 - fail
Step 3 - pass
Step 4 - pass

Yes, I remarked that when the plugin was modified in 3.9 for security reasons.
It will be merged in 4.0 with this new code.

bbdf775#diff-8ca6ae5a8651d5eb87f3bad712894457

In my test I had there refused core.create for menus to an admin.

For that case we could also add the the authorisation (core.create) for all components used in the first public function onSampledataGetOverview() therefore refusing to run the plugin when the user has no create rights for ALL the components involved.

Note : a failure for one iteration may also happen if the component concerned is NOT enabled.
Note 2 : It will be necessary anyway to make a patch for the multilingual sample data after the 3.9 commit is merged into 4.0

It can skip a step if some requirements are not met (eg if an extensions isn't installed), but that's still technically a success. If one step actually fails, the whole thing will stop and it will never go further.

I was also a bit confused about installing sample content:
the progress bar is animated, and keeps "moving" even after the installation has been completed.

<div class="progress">
	<div class="progress-bar progress-bar-striped progress-bar-animated bg-success" role="progressbar" aria-valuemin="0" aria-valuemax="100" aria-valuenow="100" style="width: 100%;">4/4</div>
</div>

Can't we remove the "progress-bar-animated" part with JavaScript after the installation has been finished?

better yet - remove the animated part completely as it fails a11y reduced-motion tests