Sort month that is in extensions in Postgres

I've been investigating and I think I've found a solution for you, passing every% of% of the month to its number (eg string ):

SELECT 
       CASE 
            WHEN mes = "Janeiro" THEN 1
            WHEN mes = "Fevereiro" THEN 2
            WHEN mes = "Março" THEN 3
            WHEN mes = "Abril" THEN 4
            ...
       END as meses
       , mes //apresentar também o mês em string ao lado do número
FROM tbl_meses;
ORDER BY meses ASC

If this table is just to translate the months a simple solution is to add a column with month number the ordering should be done by the year and by that new column.

If you have a date field or similar and want to display the month in full in Portuguese you can set the locale in the session and sort by month.

set lc_time = 'portuguese';
select to_char(data,'tmmonth') from tabela order by extract(year from data), extract(month from data)