Localisation settings not saving
If you interrupt the process while CiviCRM is creating the multilingual mode, you could have a corrupted database.

If you don't have access to civicrm anymore, the best way is to reload a backup of the database as mentionned by Laryn.

If you don't have any backup, i guess you could try reset the database to a monolingual by calling the function :

CRM_Core_I18n_Schema::makeSinglelingual($locale_to_keep)


with $locale_to_keep = 'en_US' or 'fr_CA'...

You need to build a standalone script for this.