If the document is parsed as HTML5, the language will default to JavaScript, and no attribute of any sort is required (for future reference, there is no language attribute in HTML5).
If you're catering to HTML 4.x or XHTML 1.x, the default scripting language is supposedly determined from the value of the Content-Script-Type header, whether present locally in a META/meta tag (high priority) or as an HTTP header (low priority). The type attribute is still required by HTML 4.x even if the Content-Script-Type header is present (locally or otherwise) since the default scripting language only affects how the values of attributes like onload, onclick, etc. are handled. The type attribute with "text/javascript" as the value ought to be used in the case of JavaScript instead of the language attribute unless you're catering to old browsers (e.g. IE4, NN4, perhaps IE5/Mac? ; remember that there was a version of IE6 for Windows 98, so the language attribute is definitely outdated enough).
One last bit of information: technically speaking, application/x-javascript is the correct value for JavaScript (unless it became application/javascript without me knowing), but unfortunately text/javascript is the one with the greatest support in terms of cross-browser compatibility.
