Some style guides (Chicago, MLA, etc.) have rules for how to do this; if you know that you are required to follow some specific one of these, then the advice there will be authoritative. That said, there are still several different options for how the original quotation and the translation are presented: the choice is yours, and then the various manuals may give you "implementation details" about such vital matters as the placement of punctuation. (For example, the 16th edition of the Chicago Manual of Style has extensive guidance in 13.71-13.79, but stops short of presenting the One True Method of including dual-language material.) I'm afraid I do not know which style manuals might be preferred for German-language texts.
Your basic choices are:
- Whether the original, or the translation, is the primary version.
- Whether the secondary version appears in the body text, in a footnote, or in an endnote.
In your case, you have decided that the translated version is primary, which makes sense if most readers don't care about the specific wording of the original, but may still want it to be available. You've also chosen to place the original text in a footnote, which makes sense for a "mid-length" quotation. If you only wanted to gloss a few words, it would be more natural to do this inline. If you had a more extensive quotation, then putting it in an endnote - or even an appendix - would avoid the problem of the gigantic multi-page footnote which can be so hostile to readers. So I think your choices are perfectly defensible.
In the case where both the original and the translation are from an external source, it is clear that both should be cited. Otherwise, you would not be giving due credit to the author and translator.
Here, the translation is your own, and in principle you should note it as "my translation" in whatever way is compatible with your citation style. For example, perhaps your footnote would say:
1 My translation; original: Es geht nicht ...
or perhaps you would write in text:
... the whole bakery." [DK 2009, my translation]
The specifics depend on which style guide you are following, if any.
Some of these "my translation" notes could be omitted, though that really depends on the quantity and variety of sources you are translating. If you have many translated quotations, some by you and some by others, then it would be clearer to retain the notes. If there is only one source which you quote repeatedly, then you could note "my translation" the first time and then not mention it again.
Another option is an explicit note early in the document, saying that all translations are your own unless indicated otherwise.