Attribute of
<input>
What does <input language=""> do?
Was used to indicate the scripting language used for events triggered by the input.

Not the language attribute you're looking for

There is no language attribute for the <input> element, as useful as that might be. This attribute was a proprietary feature added by Microsoft to its Internet Explorer browser. And it didn't refer to human language (English, Spanish, etc.), but to scripting language (JavaScript, VBScript). The attribute was used to identify what language should be used to interpret scripts inside the input. This barely makes sense today, as we really only use JavaScript in the browser. Additionally, it is nearly nonsensical to talk about using one language for scripts related to an input and those related to other things. (The late 1990s were a weird time for web browsers.)