org-export-default-language

org-export-default-language is a variable defined in `ox.el'.
Its value is

"en"

Documentation:
The default language for export and clocktable translations, as a string.
This may have an association in
`org-clock-clocktable-language-setup',
`org-export-smart-quotes-alist' and `org-export-dictionary'.
This option can also be set with the LANGUAGE keyword.

You can customize this variable.