I18n

1. Customise you own I18n solution.
One easy way is to overwrite app/helpers/devise_helper.rb, which is mentioned as “A simple way to show error messages for the current devise resource. If you need to customize this method, you can either overwrite it in your application helpers or copy the views to your application.” in the comment.

2. Setting default locale (config/application.rb)

config.i18n.default_locale = :sv

Brazilian Portuguese (devise.pt-BR.yml)
http://gist.github.com/924555 by @mateusg
http://gist.github.com/766771 by @phstc
http://gist.github.com/628507 by @shadow11

Catalan (devise.ca.yml):
https://gist.github.com/1002322 by @codegram and @jrom

Chinese Simplified (devise.zh-cn.yml)
http://gist.github.com/482530 by @doabit

Chinese Traditional (devise.zh-TW.yml)
https://gist.github.com/964066 by @l4u
http://gist.github.com/477126 by @gugod

Croatian (devise.hr.yml)
https://gist.github.com/991538 by @babinho

Czech (devise.cs.yml)
https://gist.github.com/889553 by @bver

Danish (devise.da.yml)
http://gist.github.com/638785 by @jgrau

Dutch (devise.nl.yml)
http://gist.github.com/448125 by @wilco

English (default)
http://github.com/plataformatec/devise/blob/master/config/locales/en.yml

Finnish (devise.fi.yml):
https://gist.github.com/786127 by @akonan

French (devise.fr.yml):
http://gist.github.com/379988 by @tadatoshi
https://gist.github.com/871074 by @jujudellago (update for translated-views devise-1.1.2)

German (devise.de.yml)
http://gist.github.com/520859 (Sie) by @chrugail
http://gist.github.com/624775 (Du) by @mrjfk10
http://gist.github.com/960718 (Du auch) by @punkrats

Hungarian (devise.hu.yml)
http://gist.github.com/716483 by @czettnersandor

Hebrew (devise.he.yml)
http://gist.github.com/503804, by @shmichael (devise 1.0.8)

Iceland (devise.is.yml)
http://gist.github.com/856333, by @sozialhelden

Indonesian (devise.id.yml)
http://gist.github.com/754652, by @ahmy

Italian (devise.it.yml)
http://gist.github.com/443837 by @dn2k

Japanese (devise.ja.yml)
http://gist.github.com/606476 by @yhara

Lithuanian (devise.lt.yml):
http://gist.github.com/432788 by @pacifists

Malaysian (devise.my.yml):
https://gist.github.com/977606 by @iqbalhasnan

Norwegian Bokmål (devise.nb.yml):
https://gist.github.com/902531 by @bonkowski and @kjbekkelund

Persian (devise.fa.yml)
https://gist.github.com/939048 by @ryco

Polish (devise.pl.yml)
http://gist.github.com/455635 by @sickill
http://gist.github.com/487808 by @grzesiub
http://gist.github.com/891279 by @marioosh (works with devise 1.2)

Portugal Portuguese (devise.pt-PT.yml)
http://gist.github.com/579087 by @alexreisner
http://gist.github.com/1002747 by @pama

Russian (devise.ru.yml):
http://gist.github.com/428830, by @korobkov
http://gist.github.com/428668, by @sergio-fry

Spanish (devise.es.yml)
http://gist.github.com/448139 by @pacoguzman
http://gist.github.com/463944 by @eduludi

Swedish (devise.sv.yml)
http://gist.github.com/440569 by @flojon