[Koha] Set principal language

[Vitor Fernandes]

Hi there.

I've a Koha installation with portuguese and english languages
installed, but by default the OPAC and Staff Client appears in english
and then it's possible to change to Portuguese.
There is anyway to set the default language of Koha?
I want that OPAC and Staff Client appears in Portuguese and then can
change to English.

Regards.
Vitor Fernandes