Comment 3 for bug 1861481

Gunnar, yes, the live sessions are properly translated up to and including 19.04 (and of course 18.04 too).
Starting from 19.10, all child processes of lightdm have LANGUAGE=en, so the session is untranslated. But this only happens for languages that don't have the langpack installed.

Running /usr/share/language-tools/language-options in the Ubuntu 18.04 live CD does NOT show el_GR in the output though.

But if that script hasn't changed, and lightdm hasn't changed... what did change and broke this in the 19.10 live CDs? :/

I wonder if the lightdm patch changed, and it used to call locale -a, and it was changed to call the language-options script in 19.10.