Sorry for my bad English.
I am refresh installing OC 188.8.131.52b on XAMPP (opencart-master.zip - new download 27/2/2018 at GitHub). Test myself in admin page, I try to go to Backup & Restore, click the Upload button, and try to select a file that does not have the .sql extension, I see OC show a message that missed the text - error_filetype
Please check and fix. Thanks.