If you look into deep learning, I think you'll quickly learn that the programming language doesn't matter that much. I think a great place to start would be the "Two Minute Papers"[1] Youtube channel. A lot of what he presents there is deep learning material, with links to the actual papers and often the source code as well as a plain English explanation of what's going on and why it's important. After looking at the source code of a handful, I think you'll realize that focusing on learning a single language won't be of any use.
I think it's also important to point out that it's not a great way to ask for help without giving some details about your background and your motives. If you've been programming in any language for quite a while, you'll need a completely different approach to "learning C++ for deep learning" than someone who's never programmed before. Likewise, if your goal is to work in the industry producing cutting edge work, you'll take a completely different approach than someone who just wants a rough understanding of the details just to satisfy your curiosity. So, without providing that context, you're going to get answers that are all over the place, almost all of which will be useless to you.