Change the name of the wp_editor tab “html/text”

Filter gettext_with_context and change the name here:

<?php # -*- coding: utf-8 -*-
/* Plugin Name: Rename 'Text' editor to 'HTML' */
add_filter( 'gettext_with_context', 'change_editor_name_to_html', 10, 4 );

function change_editor_name_to_html( $translated, $text, $context, $domain )
{
    if ( 'default' !== $domain )
        return $translated;

    if ( 'Text' !== $text )
        return $translated;

    if ( 'Name for the Text editor tab (formerly HTML)' !== $context )
        return $translated;

    return 'HTML';
}

Result