Always specify your client O/S. Although the viewer is written in Java,
there are numerous differences in how various client O/S's handle key
mapping (among other things.)
Are you testing the 2.1.2 release candidate build?
(
https://turbovnc.sourceforge.io/vnc.nightly) There are some bug fixes
relative to 2.1.1 that relate to the transmission of dead keys, so
please retest with the latest viewer. I have specifically tested
numerous international keyboard layouts in the past week and have found
no issues with dead keys, although there were some issues in the 2.1.1
viewer. If you can still reproduce the problem with the 2.1.2 RC build,
then I'll investigate.
DRC