upgrade to 2.8 from 2.6 gives fatal error

Fatal error: Class ‘Translations’ not found in /home/p14l39fs/public_html/wordpress/wp-includes/l10n.php on line 408

Sorry to whine, but I need help and the one kind response wasn’t helpful.

I have pomo directory in my includes folder.

In pomo I have translations, streams, po, mo, and entry.php files

‘would really appreciate learning not just the fix, but WHY my careful copying of files didn’t work…

Thanks to all again.