How to unify three separate tables having same data, same columns but tuples in different languages. Only one key(caption) is common to all This needs to be done in order to complete the unification of many tables present in different databases with different languages. (Part of Dictionary Management, will have caption and messages where multiple columns can make messages)
If I understand your question correctly this is a possible solution. If not, could you please describe your problem more precisely?

To unify 3 tables to one virtual table you can create a view which has the following select query:

select 'en' lang, col1, col2, col3, col4, ... from table1
union all
select 'ru' lang, col1, col2, col3, col4, ... from table2
union all
select 'es' lang, col1, col2, col3, col4, ... from table3


If you need to modify the data in these 3 tables as well you have to know where the data came from. This is why I added the column "lang" -- perhaps it already exists.
With an instead-of triggers you can also manipulate the data in the table even though you insert/update/delete the view.

So here is an example:

update view set col4 = 'asdf' where lang = 'en' and col1 = 12345;


--> In the instead-of trigger you can then rewrite the update to the actual table:

update table1 set col4 = 'asdf' where col1 = 12345;