language="javascript" vs. type="text/javascript"

The language attribute is deprecated. Use type only. You don't need to specify type in HTML5, it's javascript per default.

<script language="javascript"> was used in very old browsers, and is deprecated.

<script type="text/javascript"> is the HTML 4 standard.

In HTML 5, the type parameter is optional (text/javascript is the default), so you can just do <script>.

As a neat hack, if you put an invalid type, the script won't be ran, but you can still read the data in JavaScript. Some template libraries do this.