Getting the top count of records from a table for each month and user
Due to lack of windows functions and cte, mysql version is quite verbose, but I hope it will give you desired results in reasonable time (I know it's not fast at all):

SELECT a.*, c.*
FROM 
(
   SELECT yr,mn, MAX(translations_per_month) as max_user_translations
   FROM
   (
     SELECT  YEAR(`date_added`) as yr, MONTH(`date_added`) as mn, user_id, 
     COUNT(1) as translations_per_month
     FROM `gp_translations` t1
     INNER JOIN gp_users u ON 
      (u.id = t1.user_id AND u.STATUS='current' OR u.STATUS='old')
     GROUP BY  YEAR(`date_added`), MONTH(`date_added`),user_id
    )b
    GROUP BY yr,mn
)a
INNER JOIN 
(
   SELECT  YEAR(`date_added`) as yr, MONTH(`date_added`) as mn, user_id, display_name,
   COUNT(1) as translations_per_month
   FROM `gp_translations` t1
   INNER JOIN gp_users u ON (u.id = t1.user_id AND u.STATUS='current' OR u.STATUS='old')
   GROUP BY YEAR(`date_added`), MONTH(`date_added`),user_id, display_name
)c ON  (c.yr = a.yr and c.mn = a.mn and c.translations_per_month = a.max_user_translations)


Also, I made a guess that status column is in gb_users table ; if not, the query needs to be modified a bit.