Improve pop-up description for file icons

Previously, we used an hardcoded 'file icon' string, replaced with
$s_file_icon_description.

Also, added new $s_unknown_file_extension string to have a descriptive
text when the file extension is not referenced in $g_file_type_icons
instead of just displaying '?'.

Fixes #27827

core/file_api.php

@@ -341,8 +341,10 @@ function file_get_icon_url( $p_display_filename ) {
 		$t_ext = '?';
 	}
 
-	$t_name = $t_file_type_icons[$t_ext];
-	return array( 'url' => $t_name, 'alt' => $t_ext );
+	return array(
+		'url' => $t_file_type_icons[$t_ext],
+		'alt' => $t_ext == '?' ? lang_get( 'unknown_file_extension' ) : $t_ext
+	);
 }
 
 /**

core/print_api.php

@@ -1785,7 +1785,7 @@ function print_file_icon( $p_filename ) {
 	print_icon(
 		string_attribute( $t_icon['url'] ),
 		'',
-		string_attribute( $t_icon['alt'] ) . ' file icon'
+		sprintf( lang_get( 'file_icon_description' ), string_attribute( $t_icon['alt'] ) )
 	);
 }
 

lang/strings_english.txt

@@ -602,6 +602,8 @@ $s_last_edited = 'Last edited:';
 # file_api.php
 $s_hide_content = 'Hide Content';
 $s_show_content = 'Show Content';
+$s_file_icon_description = '%1$s file icon';
+$s_unknown_file_extension = 'unknown';
 
 # html_api.php
 $s_webmaster_contact_information = 'Contact <a href="mailto:%1$s" title="Contact the webmaster via e-mail.">administrator</a> for assistance';