Hi,

> +               (wrap-program (string-append out "/bin/AusweisApp2")
> +                 `("QT_PLUGIN_PATH" ":" prefix
> +                   ,(map (lambda (label)
> +                           (string-append (assoc-ref inputs label)
> +                                          "/lib/qt5/plugins"))
> +                         '("qtbase" "qtdeclarative"
> +                           "qtsvg" "qtwebsockets")))
> +                 `("QML2_IMPORT_PATH" ":" prefix
> +                   ,(map (lambda (label)
> +                           (string-append (assoc-ref inputs label)
> +                                          "/lib/qt5/qml"))
> +                         '("qtdeclarative" "qtgraphicaleffects"
> +                           "qtquickcontrols2" "qtsvg"))))

There is procedure 'wrap-qt-program' in (guix build qt-utils).
It should set QML2_IMPORT_PATH, QT_PLUGIN_PATH, XDG_DATA_DIRS and
XDG_CONFIG_DIRS appropriately. (Actually, wrap-qt-program's usage
of 'getenv' when cross-compiling looks incorrect to me, but that's a
separate issue.)

Perhaps you could use 'wrap-qt-program' instead of 'wrap-program'?
See, e.g., the package definition of qbittorrent.

Greetings,
Maxime.