Expression #1 of SELECT list is not in GROUP BY clause and contains nonaggregated column 'corancor_website.b.id' which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by
SELECT b.*, vc.content AS title, lt.content AS content FROM `boxes` AS b LEFT JOIN content_vc AS vc ON (vc.id=b.title_ref AND vc.lang = 'rus') LEFT JOIN content_lt AS lt ON (lt.id=b.content_ref AND lt.lang = 'rus') WHERE (b.lang='rus' OR b.location='') AND b.location<>'e0' GROUP BY b.location ORDER BY RAND();