TL;DR in /etc/profile set:
About each variable:
Other variables (that probably no one wants to enable).
- export GTK_MODULES=gail:atk-bridge
Not included because it's deprecated.
- export GNOME_ACCESSIBILITY=1
Haven't been used by applications for a very long time.
- export QT_ACCESSIBILITY=1
All guides mention it but it was removed a really long time ago (in 2011).
Alternative solution for Qt:
If "accessibility" use flag is set (for dev-qt/qtgui or dev-qt/qtbase), install an env.d file that exports QT_LINUX_ACCESSIBILITY_ALWAYS_ON=1.
+ Guaranteed not to break applications (e.g. due to missing DBus -- needs testing)
- Can't be controlled on per-slot basis, it'll be global anyway.