app/views/user_profile/_form.html.erb
<%= simple_form_for current_user, url: profile_path do |f| %>
<% if current_user.errors.any? %>
<div id="error_explanation">
<h2>
<%= pluralize(current_user.errors.count, "error") %> prohibited
this user from being saved:
</h2>
<ul>
<% current_user.errors.full_messages.each do |msg| %>
<li><%= msg %></li>
<% end %>
</ul>
</div>
<% end %>
<%= f.input :email, as: :string %>
<%= f.input :password %>
<%= f.input :locale, collection: I18n.available_locales %>
<%= f.button :submit %>
<% end %>