perturbation in czech perturbation in german perturbation in danish perturbation in spanish perturbation in french perturbation in norwegian perturbation in russian perturbation in swedish perturbation in bulgarian perturbation in belarusian perturbation in estonian perturbation in finnish perturbation in greek perturbation in croatian perturbation in hungarian perturbation in portuguese perturbation in slovak perturbation in ukrainian perturbation in polish perturbation in albanian perturbation in lithuanian perturbation in romanian