1-) 1.
Will the Tunisian court also decide about the civil damages? This is important, because if the Tunisian court also decides about the civil case, then the German lawsuit concerning the civil damages would be inadmissible.
===> In theory, the court of competent jurisdiction in this business is the Tunisian court of the place of the accident. This court decides penal question as of the civil liability which includes/understands the question of the damages.
2- 2.
The motorbike was insured by a Tunisian insurance company. How can the insurance company be involved in the lawsuit?
====> In theory, the civilly responsible one in this business is the policy-holder who is charged with the motor cycle (generally the hotel). Thus, the German citizen could call upon the intervention of assured which, itself, will call upon its insurance company which will have to answer of the question of the damages.
I hope that my English readable because that is made a good moment that I did not practise it. Moreover, I be rather null in English language