I can confirm your problem with all keyboard layouts that use dead-keys.
The Spanish layout uses dead keys to type certain characters.
As you say in a comment:
I type " ´ " and then " e ", resulting in " é "
My favorite solution is:
sudo apt install language-selector-gnome
From Applications/Slingshot launch 'Language Support' (gnome-language-selector
- part of language-selector-gnome
).
Set 'Keyboard method input system' to 'XIM'.

Log out and back.
This problem seems partially related to this askubuntu question: Dead keys (accents) stopped working after upgrading to Ubuntu 16.04 and even to this bug which refers to Spanish, with the notable difference that here only Skype is affected.
As indicated here, this may seem related to a more general problem affecting Qt applications. Trying the solution thereunder (install and run qtconfig-qt4
, go to the Interface tab,under Default Input Method, select ibus) it doesn't seem to work. (Initially only xim
is available there, not ibus
; but that option appears after installing ibus-qt4
. Enabling that option doesn't fix our problem though.) - Possibly this is not a qt
issue.
There seems to be a temporary fix indicated in the answer under the askubuntu linked question that says to open a terminal and type ibus-setup
.
I did that and got this:

Then I pressed Yes and got this:

As those settings doesn't seem available in elementary, I just went to Skype and now the dead keys work.
But only before logout.
It seems the ibus service is installed but elementary doesn't need that, while Skype needs it. You can start it with your session (according to How to add iBus to start up applications?) by going to Settings-Applications-Startup, press the plus in the left down corner and add the command
ibus-daemon --xim
.
(Adding just ibus-daemon
as indicated in another answer under that linked question doesn't fix it.).
ibus-qt4
doesn't fix this at all, whileibus-daemon --xim
at startup fixes it withoutibus-qt4
being installed. -- Dead-keys is obviously a different problem; even if the two had the same cause (like this bug) they are still separated. - Both solutions that I have posted work and none seems to concernqt
, but are maybe closer to this bug involvinggnome-language-selector
.