Phoenix date_select フォーマット

[ruby]
<div class="form-group">
<%= label f, :birthday, class: "control-label" %>
<%= date_select f, :birthday, default: :calendar.local_time(), builder: fn b -> %>
<%= b.(:month, [
options: [
{gettext("1月"), "1"},
{gettext("2月"), "2"},
{gettext("3月"), "3"},
{gettext("4月"), "4"},
{gettext("5月"), "5"},
{gettext("6月"), "6"},
{gettext("7月"), "7"},
{gettext("8月"), "8"},
{gettext("9月"), "9"},
{gettext("10月"), "10"},
{gettext("11月"), "11"},
{gettext("12月"), "12"},
]
]) %>
<% end %>
<%= error_tag f, :birthday %>
</div>
[/ruby]