I'm running Emacs 26.3 on Ubuntu 20.04.3 LTS in a WSL1 container on a Windows laptop, using MobaXterm's X server to provide the display.
Using "Options > Set Default Font..." I select "DejaVu Sans Mono Book" and the font in my buffers changes, but none of the italic faces show as that - they're all still upright. Furthermore, if I select "DejaVu Sans Mono Italic" as the font then the preview on the "Pick a font" popup shows the slanted font correctly, but everything in my buffers is still upright.
After doing "Options > Save Options", the "custom-set-faces" call in my options file contains
'(default ((t (:family "DejaVu Sans Mono" :foundry "PfEd" :slant normal :weight normal :height 98 :width normal))))
and if I change this to have
:family "Courier" :foundry "Adobe" and restart emacs then I do get slanted italics, but the text is a bit small and tweaking the "98" just breaks it.
I do get italics when I select "Nimbus Mono PS" as the font, but that's weird because according to xlsfonts I don't have that one installed!
All I all I'm thoroughly confused. Can anyone shed any light?