Add number localization to Rails' `i18n` module.

localize_helper.rb

module LocalizeHelper

  # Wraps I18n.localize to add support for Numbers l12n.
  #
  # @param  value [Numeric|DateTime|Time|Date] The value to localize.
  # @return [String] The localized value.
  # @see  <https://github.com/svenfuchs/i18n/issues/135>
  def localize(value)
    if value.is_a?(Numeric)
      number_with_delimiter(value, locale: I18n.locale)
    else
      I18n.l(value)
    end
  end

  # Override the global `l` alias for localization.
  alias_method :l, :localize
end

localize_helper_spec.rb

require 'spec_helper'

describe LocalizeHelper do
  let(:locale) { 'en' }

  before { I18n.locale = locale }
  after  { I18n.locale = 'en' }

  subject { localize target }

  context 'on a number' do
    let(:target) { 9000 }

    context 'in English' do
      it { should == '9,000' }
    end

    context 'in French' do
      let(:locale) { 'fr' }

      it { should == '9 000' }
    end
  end

  context 'on a date' do
    let(:target) { Date.new(2001, 2, 3) }

    context 'in French' do
      let(:locale) { 'fr' }

      it { should == '03/02/2001' }
    end
  end
end

Great idea but I18n.localize can take more arguments than just the value.
As such the method you propose will fail if you require some specific format when localizing a date for example with I18n.l(adate, :format => :short) . The code can be improved, but I decided to just add a new method not tied to I18n.localize to avoid conflicts.

def ln(value)
    number_with_delimiter(value, locale: I18n.locale)
end