My Swedish based keyboard layout. I did a frequency analysis for some different texts including some source code, and tried to add the most-used of the harder-to-reach characters in nice places, with paired characters also next to each other on the same level. Then I added some extra stuff just-in-case, and combination characters for pinyin Chinese (and romanizing Japanese). The right thumb on AltGr is the real MVP here.
There is room to spare; I considered adding some more keys, like mathematical symbols, but it's probably best to use some compose key functionality – WinCompose looks good for Windows.
Via Keyboard Layout Editor, as compared to Windows 10's ordinary Swedish layout on an ISO 105 keyboard. Gray key labels denote keys that are unchanged; dead keys are marked as such; and some keys have clarifying text beneath.
(KLE link.)
Pressing Shift. (KLE link.)
Pressing AltGr. I use macron to write Japanese words like "Tōkyō". (KLE link.)
Other than the expected composites, the Windows layout also has these for the macron key: you can press n for – ("en dash"), m for — ("em dash"), ! for ‽ ("interrobang"), - for ‑ ("non-breaking hyphen"), _ for ("soft hyphen"), : for · ("interpunct"), c for ©, r for ®, t for ™, / for ÷, = for ≡, or (plain space) for ("non-breaking space").
Pressing both Shift (left or right) and AltGr (alternatively Alt and left or right Ctrl). "Soft" is a soft hyphen, "nbsp" is a non-breaking space. I use the "tones" to write the tones of pinyin like "Àishāníyǎ". (KLE link.)
I don't know why anybody else would want my layout, but on Windows you could download Microsoft Keyboard Layout Creator, open the .klc file, and generate the installation files. Alternatively, you could download a compressed release and install that one if you trust me. As for Linux, what I personally did was to run sudo curl https://raw.githubusercontent.com/dnym/kbdlayout/main/chiral.xkb --output /usr/share/X11/xkb/symbols/custom and then select something like "user-defined custom layout" in whatever keyboard settings are used.