<% if attachable.respond_to?(:translated_locales) && attachable.translated_locales.many? %>
  <%= form.label :locale, 'This attachment displays in' %>
  <%= form.select :locale, options_for_locales(attachable.translated_locales), include_blank: 'All languages' %>
<% end %>
<%= form.text_field :isbn, label_text: 'ISBN' %>
<%= form.text_field :unique_reference %>
<div class="paper-number clearfix">
  <%= form.text_field :command_paper_number, class: 'paper-number' %>
  <%= form.check_box :unnumbered_command_paper, label_text: 'Unnumbered' %>
</div>
<% if attachable.can_have_attached_house_of_commons_papers? %>
  <%= render 'admin/attachments/hoc_reference_fields', form: form %>
<% end %>
<%= form.text_field :order_url, label_text: 'Order URL' %>
<%= form.text_field :price, label_text: "Price in £s" %>

<% if attachable.respond_to?(:translated_locales) && attachable.translated_locales.many? %>
  <%= form.label :locale, 'Display language' %>
  <p class="help-block">This determines the translations of the publication that the attachment will appear in.</p>
  <%= form.select :locale, options_for_locales(attachable.translated_locales), include_blank: 'All languages' %>
<% end %>
<%= form.text_field :isbn, label_text: 'ISBN' %>
<%= form.text_field :unique_reference %>
<div class="paper-number clearfix">
  <%= form.text_field :command_paper_number, class: 'paper-number' %>
  <%= form.check_box :unnumbered_command_paper, label_text: 'Unnumbered' %>
</div>
<% if attachable.can_have_attached_house_of_commons_papers? %>
  <%= render 'admin/attachments/hoc_reference_fields', form: form %>
<% end %>
<%= form.text_field :order_url, label_text: 'Order URL' %>
<%= form.text_field :price, label_text: "Price in £s" %>

Update locale label on attachment edit form
Update locale label on attachment edit form

To clarify the purpose of the language field.
