Thanks for creating this issue.
The file types are not being displayed at the moment because there is no string identifier for the mimetypes of those files (basically we don't have a string to describe those file types).
The docx/xlsx... file types are a very good candidate to translate however there are lots of other mime types that we havn't translated.
I suppose at some point we will need to decide which to translate for.
To get this issue kick started the following patch introduces strings for a few more file types.
diff --git a/lang/en/mimetypes.php b/lang/en/mimetypes.php
index 17d224e..052e326 100644
@@ -25,8 +25,14 @@
$string['application/msword'] = 'Word document';
$string['application/pdf'] = 'PDF document';
+$string['application/vnd.moodle.backup'] = 'Moodle backup';
$string['application/vnd.ms-excel'] = 'Excel spreadsheet';
$string['application/vnd.ms-powerpoint'] = 'Powerpoint presentation';
+$string['application/vnd.openxmlformats-officedocument.presentationml.presentation'] = 'Powerpoint presentation';
+$string['application/vnd.openxmlformats-officedocument.presentationml.slideshow'] = 'Powerpoint slideshow';
+$string['application/vnd.openxmlformats-officedocument.spreadsheetml.sheet'] = 'Excel spreadsheet';
+$string['application/vnd.openxmlformats-officedocument.spreadsheetml.template'] = 'Excel template';
+$string['application/vnd.openxmlformats-officedocument.wordprocessingml.document'] = 'Word document';
$string['application/zip'] = 'zip archive';
$string['audio/mp3'] = 'MP3 audio file';
$string['audio/wav'] = 'sound file';
@@ -35,5 +41,6 @@ $string['image/bmp'] = 'uncompressed BMP image';
$string['image/gif'] = 'GIF image';
$string['image/jpeg'] = 'JPEG image';
$string['image/png'] = 'PNG image';
+$string['text/html'] = 'HTML document';
$string['text/plain'] = 'text file';
-$string['text/rtf'] = 'RTF document';
+$string['text/rtf'] = 'RTF document';
\ No newline at end of file
As well as that we should consider adding upgrade code to re-parse the resource records in the database and updating the field that caches that information for each resource.
If we only add the strings then in order for the type to be displayed a teacher or such will have to edit and save each resource.
Perhaps given this information isn't essential that is fine, however still to be considered.
Marking this triaged and with a patch.