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)