Error from Date in Print Format

This error is happening on print formats in the Sales Order & Delivery Note, is caused by the date field:

Traceback (most recent call last):
  File "/home/erpuser/frappe-bench/apps/frappe/frappe/app.py", line 55, in application
    response = frappe.handler.handle()
  File "/home/erpuser/frappe-bench/apps/frappe/frappe/handler.py", line 19, in handle
    execute_cmd(cmd)
  File "/home/erpuser/frappe-bench/apps/frappe/frappe/handler.py", line 36, in execute_cmd
    ret = frappe.call(method, **frappe.form_dict)
  File "/home/erpuser/frappe-bench/apps/frappe/frappe/__init__.py", line 876, in call
    return fn(*args, **newargs)
  File "/home/erpuser/frappe-bench/apps/frappe/frappe/www/print.py", line 160, in get_html_and_style
    no_letterhead=no_letterhead, trigger_print=trigger_print),
  File "/home/erpuser/frappe-bench/apps/frappe/frappe/www/print.py", line 139, in get_html
    html = template.render(args, filters={"len": len})
  File "/home/erpuser/frappe-bench/env/local/lib/python2.7/site-packages/jinja2/environment.py", line 989, in render
    return self.environment.handle_exception(exc_info, True)
  File "/home/erpuser/frappe-bench/env/local/lib/python2.7/site-packages/jinja2/environment.py", line 754, in handle_exception
    reraise(exc_type, exc_value, tb)
  File "/home/erpuser/frappe-bench/apps/frappe/frappe/./templates/print_formats/standard.html", line 28, in top-level template code
    {{ render_field(df, doc) }}
  File "/home/erpuser/frappe-bench/apps/frappe/frappe/./templates/print_formats/standard_macros.html", line 9, in template
    {{ render_field_with_label(df, doc) }}
  File "/home/erpuser/frappe-bench/apps/frappe/frappe/./templates/print_formats/standard_macros.html", line 65, in template
    {{ print_value(df, doc) }}{% endif %}
  File "/home/erpuser/frappe-bench/apps/frappe/frappe/./templates/print_formats/standard_macros.html", line 97, in template
    {{ doc.get_formatted(df.fieldname, parent_doc or doc, translated=True) }}
  File "/home/erpuser/frappe-bench/apps/frappe/frappe/model/base_document.py", line 645, in get_formatted
    return format_value(val, df=df, doc=doc, currency=currency)
  File "/home/erpuser/frappe-bench/apps/frappe/frappe/utils/formatters.py", line 24, in format_value
    return formatdate(value)
  File "/home/erpuser/frappe-bench/apps/frappe/frappe/utils/data.py", line 211, in formatdate
    return babel.dates.format_date(date, format_string, locale=(frappe.local.lang or "").replace("-", "_"))
  File "/home/erpuser/frappe-bench/env/local/lib/python2.7/site-packages/babel/dates.py", line 565, in format_date
    locale = Locale.parse(locale)
  File "/home/erpuser/frappe-bench/env/local/lib/python2.7/site-packages/babel/core.py", line 315, in parse
    raise UnknownLocaleError(input_id)
UnknownLocaleError: unknown locale u'loading'

Does anyone have any idea why this is happening?

Should be the bug in python-babel-localedata package: https://bugs.launchpad.net/ubuntu/+source/python-babel/+bug/1299442
Reinstallation should fix it.