Hi Armin!

In my humble opinion, I'd say that it would be better to use only one language to learn Spanish. I mean, you can use English to learn both French and Spanish, but since your native language is German, I think you are mixing a lot of languages and that can be a bit messy. But if you are quite fluent in French as well (as I can see in your profile), another approach could be learning Spanish with a teacher who can speak French. I hope this helps ;)