I couldn't go in the BO because of that error. admin employee has EN lang but site has RO.
For me helped these steps:
1) on DB change en-US (id1) to RO (default shop lang, id2)
UPDATE `pseg_employee` SET `id_lang` = '2' WHERE `pseg_employee`.`id_employee` = 3;
2) After that remove EN lang in the International > Localization > tab Languages (maybe try just update lang pack without delete)
3) Import EN (in my case United states) language pack International > Localization > first tab
4) enable EN lang for admin employee.
Best regards 