Input method change in GNU IceCat installed via Guix

[Zelphir Kaltstahl]

Hi Guix Users!

Recently I installed GNU IceCat via Guix. A few days ago I noticed
something:

I cannot switch input method when the GNU IceCat window is focused. My
shortcut was CTRL+tilde before and I already tried changing it to the
more common CTRL+ALT+space, but that also does not work. To me it seems,
that IceCat does not bubble up the keyboard event for this shortcut to
the system and then the system (Xubuntu 18.04) does not notice, that I
pressed the input method switching shortcut. But that is only a guess,
as I do not really know how the order of keyboard event processing is
organized.

If it was only switching a few characters on the keyboard, I could live
with simply typing differently, but when I want to input Chinese
characters, I currently need to open another program, any text editor
not having this issue, and then type there and copy paste it into IceCat.

I am using Fcitx for input method management. My GNU IceCat version is
`60.3.0esr (64-bit)`.

Another application where it does not work is Emacs. However, there the
useful built-in IM exists which can be switched to by: `C-u
C-<backslash> chinese-py <return>` so I do not need it there.

What can I do to make IM switching work when IceCat is focused?

Regards,

Zelphir