<meta name="language" content="Spanish">
This isn't defined in any specification (including the HTML5 draft)
<meta http-equiv="content-language" content="es">
This is a poor man's version of a real HTTP header and should really be expressed in the headers. For example:
Content-language: es
Content-type: text/html;charset=UTF-8
It says that the document is intended for Spanish language speakers (it doesn't, however mean the document is written in Spanish; it could, for example, be written in English as part of a language course for Spanish speakers).
From the spec:
The Content-Language entity-header field describes the natural language(s) of the intended audience for the enclosed entity. Note that this might not be equivalent to all the languages used within the entity-body.
If you want to state that a document is written in Spanish then use:
<html lang="es">
与恶龙缠斗过久,自身亦成为恶龙；凝视深渊过久,深渊将回以凝视…
