I've seen post describing that but they are marked as resolved. But I tried all methods listed here:
- switching to the Twenty Eleven theme by renaming your current theme's folder inside wp-content/themes and adding "-old" to the end of the folder name using FTP or whatever file management application your host provides.
- resetting the plugins folder by FTP or phpMyAdmin.
- re-uploading all files & folders - except the wp-content folder - from a fresh download of WordPress.
- running the upgrade manually via wp-admin/upgrade.php
None of them works - I tested it on a couple of different sites.
Tricky thing - one site was upgraded before the translated edition (PL) was ready, and then the admin was ok. But in all other cases, where site was upgraded in translated edition, the upgrade process gave broken admin.