[Xfce-i18n] error message of unknown origin not understood

[Benno Schulenberg]

Hello,

On an Xfce install (localized to Dutch), my sister sees the following
message after an automatic login to the desktop:

  systeemprogrammeerprobleem ontdekt

I have no idea what this means, nor which part of Xfce produces this
message (if it is some part of Xfce).  The git repos (which include
the PO files) do not seem to be searchable: a websearch for the string
gives zero results.

Does anyone have the whole of Xfce checked out and can grep for the
above string?

Cheers,

Benno