It really can be solved just to updating locale collumn from NULL to a valid locale, how was informed in https://forum.pkp.sfu.ca/t/ojs-3307-an-unexpected-error-has-occurred-array-to-string-conversion-in-core-pkpstring-inc-php-on-line-421/69243
For example: (for my country)
UPDATE submissions s SET s.locale = 'pt_BR' WHERE locale IS NULL