Download the free audio files manually from the page of the individual product, click on "Audiodatei manuell herunterladen", e.g. from Weltatlas book, and another right click on the "Klicken Sie mit der rechten Maustaste auf folgenden Link: Audiodatei zu ..." from the opened overlayed window and with "save links as" to your hard drive or directly to the connected Tiptoi (see 3.).
Connect the Tiptoi with the USB cable, turn it on. It will appear as new drive "tiptoi" in your file browser (e.g. Nautilus, Nemo, Thunar).
Transfer the downloaded audio files from your harddrive to your tiptoi drive without changing the name (e.g. in your file browser).
Best Answer
The link to the firmware download has changed and is now here https://www.ravensburger.de/entdecken/ravensburger-marken/tiptoi/Aktualisierung-der-Firmware/index.html
One person every 5 years will find this useful. ;-p