1 Changing the interface to English

Create the file config/locales/pt-BR.yml and paste the following content there:

pt-BR:
  # formatos de data e hora
  date:
    formats:
      default: "%d/%m/%Y"
      short: "%d de %B"
      long: "%d de %B de %Y"

    day_names: [Domingo, Segunda, Terça, Quarta, Quinta, Sexta, Sábado]
    abbr_day_names: [Dom, Seg, Ter, Qua, Qui, Sex, Sáb]
    month_names: [~, Janeiro, Fevereiro, Março, Abril, Maio, Junho, Julho, Agosto, Setembro, Outubro, Novembro, Dezembro]
    abbr_month_names: [~, Jan, Fev, Mar, Abr, Mai, Jun, Jul, Ago, Set, Out, Nov, Dez]
    order: [day, month, year]

  time:
    formats:
      default: "%A, %d de %B de %Y, %H:%M h"
      short: "%d/%m, %H:%M h"
      long: "%A, %d de %B de %Y, %H:%M h"
    am: ''
    pm: ''

  # distancia do tempo em palavras
  datetime:
    distance_in_words:
      half_a_minute: 'meio minuto'
      less_than_x_seconds:
        one: 'menos de 1 segundo'
        other: 'menos de %{count} segundos'

      x_seconds:
        one: '1 segundo'
        other: '%{count} segundos'

      less_than_x_minutes:
        one: 'menos de um minuto'
        other: 'menos de %{count} minutos'

      x_minutes:
        one: '1 minuto'
        other: '%{count} minutos'

      about_x_hours:
        one: 'aproximadamente 1 hora'
        other: 'aproximadamente %{count} horas'

      x_days:
        one: '1 dia'
        other: '%{count} dias'

      about_x_months:
        one: 'aproximadamente 1 mês'
        other: 'aproximadamente %{count} meses'

      x_months:
        one: '1 mês'
        other: '%{count} meses'

      about_x_years:
        one: 'aproximadamente 1 ano'
        other: 'aproximadamente %{count} anos'

      over_x_years:
        one: 'mais de 1 ano'
        other: 'mais de %{count} anos'

      almost_x_years:
        one: 'quase 1 ano'
        other: 'quase %{count} anos'

    prompts:
      year:   "Ano"
      month:  "Mês"
      day:    "Dia"
      hour:   "Hora"
      minute: "Minuto"
      second: "Segundos"

  # numeros
  number:
    format:
      precision: 3
      separator: ','
      delimiter: '.'
    currency:
      format:
        unit: 'R$'
        precision: 2
        format: '%u %n'
        separator: ','
        delimiter: '.'
    percentage:
      format:
        delimiter: '.'
    precision:
      format:
        delimiter: '.'
    human:
      format:
        precision: 2
        delimiter: '.'
        significant: true
        strip_unsignificant_zeros: true
      # number_to_human_size()
      storage_units:
        format: "%n %u"
        units:
          byte:
            one: "Byte"
            other: "Bytes"
          kb: "KB"
          mb: "MB"
          gb: "GB"
          tb: "TB"
      # number_to_human()
      # new in rails 3: please add to other locales
      decimal_units:
        format: "%n %u"
        units:
          unit: ""     
          thousand: "mil"
          million:
            one: milhão
            other: milhões
          billion:
            one: bilhão
            other: bilhões
          trillion:
            one: trilhão
            other: trilhões
          quadrillion:
            one: quatrilhão
            other: quatrilhões

  # Usado no Array.to_sentence
  support:
    array:
      words_connector: ", "
      two_words_connector: " e "
      last_word_connector: " e "

  # ActiveRecord
  activerecord:
    errors:
      template:
        header:
          one: "Não foi possível gravar %{model}: 1 erro"
          other: "Não foi possível gravar %{model}: %{count} erros."
        body: "Por favor, verifique o(s) seguinte(s) campo(s):"
      messages:
        inclusion: "não está incluído na lista"
        exclusion: "não está disponível"
        invalid: "não é válido"
        confirmation: "não está de acordo com a confirmação"
        accepted: "deve ser aceito"
        empty: "não pode ficar vazio"
        blank: "não pode ficar em branco"
        too_long: "é muito longo (máximo: %{count} caracteres)"
        too_short: "é muito curto (mínimo: %{count} caracteres)"
        wrong_length: "não possui o tamanho esperado (%{count} caracteres)"
        taken: "já está em uso"
        not_a_number: "não é um número"
        not_an_integer: "não é um número inteiro"
        greater_than: "deve ser maior do que %{count}"
        greater_than_or_equal_to: "deve ser maior ou igual a %{count}"
        equal_to: "deve ser igual a %{count}"
        less_than: "deve ser menor do que %{count}"
        less_than_or_equal_to: "deve ser menor ou igual a %{count}"
        odd: "deve ser ímpar"
        even: "deve ser par"
        record_invalid: "A validação falhou: %{errors}"

Then go to config/application.rb and add the content below. This makes Brazilian Portuguese the default language of the application.

config.i18n.default_locale = :"pt-BR"
I18n.enforce_available_locales = false

2 Changing pluralization to Portuguese

The file config/initializers/inflections.rb is responsible for telling Rails how it should pluralize/singulate names. Change it to the following content:

# encoding: utf-8
# Be sure to restart your server when you modify this file.

# Add new inflection rules using the following format
# (all these examples are active by default):
# ActiveSupport::Inflector.inflections do |inflect|
#   inflect.plural /^(ox)$/i, '\1en'
#   inflect.singular /^(ox)en/i, '\1'
#   inflect.irregular 'person', 'people'
#   inflect.uncountable %w( fish sheep )
# end
ActiveSupport::Inflector.inflections do |inflect|
  inflect.clear

  inflect.plural(/$/,  's')
  inflect.plural(/(s)$/i,  '\1')
  inflect.plural(/^(paí)s$/i, '\1ses')
  inflect.plural(/(z|r)$/i, '\1es')
  inflect.plural(/al$/i,  'ais')
  inflect.plural(/el$/i,  'eis')
  inflect.plural(/ol$/i,  'ois')
  inflect.plural(/ul$/i,  'uis')
  inflect.plural(/([^aeou])il$/i,  '\1is')
  inflect.plural(/m$/i,   'ns')
  inflect.plural(/^(japon|escoc|ingl|dinamarqu|fregu|portugu)ês$/i,  '\1eses')
  inflect.plural(/^(|g)ás$/i,  '\1ases')
  inflect.plural(/ão$/i,  'ões')
  inflect.plural(/^(irm|m)ão$/i,  '\1ãos')
  inflect.plural(/^(alem|c|p)ão$/i,  '\1ães')

  # Sem acentos...
  inflect.plural(/ao$/i,  'oes')
  inflect.plural(/^(irm|m)ao$/i,  '\1aos')
  inflect.plural(/^(alem|c|p)ao$/i,  '\1aes')

  inflect.singular(/([^ê])s$/i, '\1')
  inflect.singular(/^(á|gá|paí)s$/i, '\1s')
  inflect.singular(/(r|z)es$/i, '\1')
  inflect.singular(/([^p])ais$/i, '\1al')
  inflect.singular(/eis$/i, 'el')
  inflect.singular(/ois$/i, 'ol')
  inflect.singular(/uis$/i, 'ul')
  inflect.singular(/(r|t|f|v)is$/i, '\1il')
  inflect.singular(/ns$/i, 'm')
  inflect.singular(/sses$/i, 'sse')
  inflect.singular(/^(.*[^s]s)es$/i, '\1')
  inflect.singular(/ães$/i, 'ão')
  inflect.singular(/aes$/i, 'ao')
  inflect.singular(/ãos$/i, 'ão')    
  inflect.singular(/aos$/i, 'ao')
  inflect.singular(/ões$/i, 'ão')
  inflect.singular(/oes$/i, 'ao')
  inflect.singular(/(japon|escoc|ingl|dinamarqu|fregu|portugu)eses$/i, '\1ês')
  inflect.singular(/^(g|)ases$/i,  '\1ás')

  # Incontáveis
  inflect.uncountable %w( tórax tênis ônibus lápis fênix )

  # Irregulares
  inflect.irregular "país", "países"
end

Creating tables and controllers with names in English, you need to take a few things into consideration:

2.1 not all words will be pluralized correctly

Actually this can happen even by programming in English. Ideally, open the Rails console in your application (rails console or rails c) and check for pluralization.

For example: type "usuario".pluralize and check if the output is "usuarios". Then type "usuarios".singularize and check if the output is "usuario".

To avoid problems, if Rails is pluralizing wrong, before creating the tables and controllers include the following line in inflections.rb to force the correct pluralization:

inflect.irregular "usuario", "usuarios"

Obs.: "usuario" is just one example, in fact it is already pluralized correctly.

2.2 caution when creating tables and controllers with more than one word in the name

Rails pluralization works by taking English into account, where adjectives come before noun. Therefore, it will only pluralize the last word of the name.

If you want to create a student grade table, do not create the template as NotaDoAluno because Rails will mistakenly pluralize as NotaDoAlunos. Instead create the template as AlunoNota, so it will pluralize as AlunoNotas. Ditto for the controllers.

If you know what you're doing, you can override the Rails table name conventions and manually configure the name of the table of that model :

class Product < ActiveRecord::Base
  self.table_name = "notas_do_aluno"
end

2.3 tables many-to-many

Sometimes you might want to create a template for a many-to-many relationship, so you can add more fields or methods. It is common that in this case the name of the two tables is in the plural, for this use in inflections.rb:

inflect.irregular "postagemtag", "postagenstags"
inflect.irregular "postagem tag", "postagens tags"
inflect.irregular "postagem_tag", "postagens_tags"

Thus, when running rails generate, it will create names of tables and controllers with both words in the plural, otherwise only the last word would be pluralized.

3 changing routes to English

This is easy, it is explained in official documentation . It will look something like this:

resources :usuarios, path_names: { new: "novo", edit: "editar" }

Or if you want you can change several at once using scope:

scope path_names: { new: "novo", edit: "editar" } do
  # seus resources
end

The variables _path are not changed, they continue with new and edit. For example: new_usuario_path and edit_usuario_path(@usuario).

Bonus-Setting Time Zone

The Rails by default displays and saves in Bank the hours in UTC time.

If you want Rails to continue saving dates / times in UTC format, but convert to the user at another time, such as Brasilia, use the code below at config/application.rb:

config.time_zone = "Brasilia"

This is a good idea if you need to support users from different countries.

But if you want Rails to both store in the bank and display to the user in Brasilia Time, use:

config.time_zone = "Brasilia"
config.active_record.default_timezone = :local

This is necessary when you are working on a legacy basis, which uses Brasilia Time in its date and Time Columns. Or if the database is your own but you import data from another database directly via SQL, without being via ActiveRecord.