Honestly, I don't think that's needed at all. I think that is a non-issue in truth. Yes we have complaints about it and we adjusted the theme by making the selection more clear. Also we have the show password field.

I don't think that having the language shown there helps anything in real world and just clutters up the ui for most users.

isn't this making the thing redundant?
if the complaints about the indicator being not noticeable are valid, that should be solved at the root, if they aren't then there is not much need of this?

As I wrote here (https://bugs.kde.org/show_bug.cgi?id=373668#c14) in my experience a combination of different things (only one of them being the keyboard layout) is responsible for wrong password entry. I believe novice users would be happy if they were given detailed hints what might be wrong (especially when they are at the login screen where it is currently not possible to run a web search to get help). From this point of view, having this RFC implemented would be step in the right direction.

For experienced users the eye button Kai mentioned here (https://bugs.kde.org/show_bug.cgi?id=373668#c15) would be good enough.

What about adding an explicit hint like this: "... Your keyboard layout is de. If in doubt use the eye button next to the password field to view your password in plain text.".

We always have to keep in mind that usind multiple layouts is an advanced feature used by a minority of users. Therefore, as long as a feature only becomes active when there are multiple layouts (and in this case only when multiple layouts are used _and_ the login failed), we do not need to worry too much about UI clutter.
For that reason, I don't see mich of an issue with the patch.

So, should I go forward with this now or abandon it?

Can it say something like "Unlocking failed. Check your keyboard layout" ? I feel it is more generic. Also, will this message show even though there is only one keyboard layout enabled? Or will it only show when there are multiple layouts?

In D3790#253155, @abetts wrote:

Also, will this message show even though there is only one keyboard layout enabled?

No

Or will it only show when there are multiple layouts?

Yes

I dunno about "Check your keyboard layout". Would we say "Check your caps lock key?" Instead, we actually show you whether your caps lock key is pressed or not.

We do have a capslock indication that shows up as soon as capslock is enabled.

I know, that's what I'm saying. For Caps Lock, we actually show the status. For this, it seems weird not to do the same. In other words, I like your original wording (or something like it) better. :)

Well, the original design also only showed it on error

Shall we land this, or are there any other objections?

Here's an idea shamelessly stolen from a blog commenter: how about showing the current keyboard layout next to the text field, instead of down in the corner? That way users would see upfront that they're using (or not using) the keyboard layout that they expect.

What does this look like now after the changes? Screenshot? Video? :D

I liked this...

Are you going to try again with a different style of notification or something?