The verbose form didn't change a thing:
> $ abiword --verbose=2
>
> ** (abiword:1646): WARNING **: Error retrieving accessibility bus address:
org.freedesktop.DBus.Error.ServiceUnknown: The name
> org.a11y.Bus was not provided by any .service files
> Aborted
But I might have found the root of the problem: As long as I am typing
without errors everything is fine. But as soon as I ignore any misspelled
word and start typing the next anyway then I can't delete any letter and
program freezes. Therefore, I disabled the on the fly spell check and the
problem disappeared.
But since Abiword didn't work initially, I installed Libre Office instead. I
didn't want to since I would prefer the theoretically much lighter Abiword
but on this old system Libre Office runs much smoother and faster. Abiword
ist very laggy and Libre Office shows the text as I am typing when Abiword is
always behind if I don't stop after some characters and wait until they
appear on screen.