Lets assume table1 contains list of country names with columns translated to English and Spanish and table2 contains only some selected countries with only English column, I want to add Spanish column. Both tables contain id country code.

Table: countries1

 code        country_english country_spanish
 AL Albania Albania
 DZ Algeria Argelia
 AD Andorra Andorra
 AO Angola Angola     

Table: countries2

 code        country_english country_spanish
 AL Albania
 AO Angola     

Result table:

 code        country_english country_spanish
 AL Albania Albania
 AO Angola Angola     
UPDATE countries2 SET `country_spanish` = (select `country_spanish` from countries1 where code = countries1.code)