What's the difference between these two meta-tags
<meta http-equiv="Content-Language" content="de, en"/> <meta name="language" content="de, en">
Are they both needed?
It's been around since HTML 4 so it's safe. Since it's just a semantic descriptor, browsers don't "fully" support it (they only need to know the character set). Google & friends understand it though, and that probably matters more.