I think Russian is easier to learn than German. It has a certain logic in the "grammatical-gender". German words have to be learned by heart to know that aspect.
BTW, here
here you can find a quite comprehensive online German grammar trainer (deutschakademie[dot]de/online-deutschkurs).
According to the page it disposes of more than 20.000 exercises sortable by most common German textbooks and grammar topics. Furthermore it features a help function, which lets you contact a GLF teacher for exercise specific support. It may take a day or so to get support by e-mail, but the service is for free.