WordPress at a glance
filter is not described

theme_templates filter-hook . WP 4.9.6

Filters list of page templates for a theme.

Usage

add_filter( 'theme_templates', 'filter_function_name_7991', 10, 4 );
function filter_function_name_7991( $post_templates, $this, $post, $post_type ){
	// filter...

	return $post_templates;
}
$post_templates(string[])
Array of page templates. Keys are filenames, values are translated names.
$this(WP_Theme)
The theme object.
$post(WP_Post/null)
The post being edited, provided for context, or null.
$post_type(string)
Post type to get the templates for.

Where the hook is called

WP_Theme::get_page_templates()
theme_templates
wp-includes/class-wp-theme.php 1082
$post_templates = (array) apply_filters( 'theme_templates', $post_templates, $this, $post, $post_type );

Where the hook is used (in WP core)

Does not used.