Ubuntu – Which US international keyboard layout gives me all umlauts and sharp S

This answer solved my problem. While I initially thought that that question dealt with an unrelated issue, it turns out that it actually is the same issue.

To summarize here, the solution is to choose the desired layout on the login screen. Then, the old layout will stop showing up and the keyboard layout indicator will be gone for good.

After some unsuccessful attempts to add my own local xkb/symbols file (see https://askubuntu.com/a/896298/883344 and https://askubuntu.com/a/896297/883344), I went for the solution from https://stackoverflow.com/a/45042841/3852630. By running

% setxkbmap -query

I see that my current layout is us. I dump this layout to my own file and make a copy

% mkdir $HOME/XKB
% cd $HOME/XKB
% xkbcomp -xkb $DISPLAY us.xkb
% cp us.xkb us-altgr-umlaut.xkb

and modified the copy as seen here

% diff us.xkb us-altgr-umlaut.xkb
1224,1225c1224,1225
<         type= "ALPHABETIC",
<         symbols[Group1]= [               u,               U ]
---
>         type= "FOUR_LEVEL_ALPHABETIC",
>         symbols[Group1]= [               u,               U,      udiaeresis,      Udiaeresis ]
1232,1233c1232,1233
<         type= "ALPHABETIC",
<         symbols[Group1]= [               o,               O ]
---
>         type= "FOUR_LEVEL_ALPHABETIC",
>         symbols[Group1]= [               o,               O,      odiaeresis,      Odiaeresis ]
1244,1245c1244,1245
<         type= "ALPHABETIC",
<         symbols[Group1]= [               a,               A ]
---
>         type= "FOUR_LEVEL_ALPHABETIC",
>         symbols[Group1]= [               a,               A,      adiaeresis,      Adiaeresis ]
1248,1249c1248,1249
<         type= "ALPHABETIC",
<         symbols[Group1]= [               s,               S ]
---
>         type= "FOUR_LEVEL_SEMIALPHABETIC",
>         symbols[Group1]= [               s,               S,          ssharp,          ssharp ]

I wrote a small shell script which is located somewhere in my search path which contains the line

xkbcomp -w 0 $HOME/XKB/us-altgr-umlaut.xkb $DISPLAY

Whenever I want to switch to my layout with German umlauts, I run this script. I switch back to the default keyboard mapping by

setxkbmap us

As mentioned in my comment above, I now use AltGr to switch a/o/u/s to ä/ö/ü/ß (decided to reprogram my brain to use AltGr instead of the Windows key which seems to have a special meaning in the Gnome 3 desktop). As described in https://blog.florianheinle.de/englische-tastatur-umlaute (in German), AltGr can be used for switching by starting gnome-tweaks, then going to Keyboard&Mouse -> Additional Layout Options -> Key to choose the 3rd level, and selecting right alt.

The alternative is of course to modify the file us in /usr/share/X11/xkb/symbols, but this may get overwritten at the next update. Anyhow, that would be the diff between the new us file and the old (same name):

26c26
<     key <AD07> {  [     u,    U, udiaeresis, Udiaeresis ] };
---
>     key <AD07> {  [     u,    U       ]   };
28c28
<     key <AD09> {  [     o,    O, odiaeresis, Odiaeresis ] };
---
>     key <AD09> {  [     o,    O       ]   };
33,34c33,34
<     key <AC01> {  [     a,    A, adiaeresis, Adiaeresis ] };
<     key <AC02> {  [     s,    S, ssharp, ssharp ] };
---
>     key <AC01> {  [     a,    A       ]   };
>     key <AC02> {  [     s,    S       ]   };