That's possible without an extension:
Open dict.cc, rightclick in the search field (of the webpage, not the address bar). select "Add a keyword for this site". Enter "d" into the input field "keyword". Save -> Done.

There is a shorter way to search dict.cc using this extension (without even opening dict.cc). Press Alt + Q. This does the same as clicking on the toolbar button of this extension.

Thanks for your review. The speed of translation depends mostly on the website of dict.cc. Not much I can do about that. If dict.cc would provide a real API, It might be possible to speed it up, but that probably won't happen anytime soon.

This is not using google translate.. it's using dict.cc. I've thought about adding more sources, but that would require a lot of changes, and thus a lot of work. Also those sources would have to agree to this (for example I wanted to add urban dictionary, but at the time, they denied my request).