diff --git a/babel/messages/catalog.py b/babel/messages/catalog.py
index b293e3c73..cd01ec4e4 100644
--- a/babel/messages/catalog.py
+++ b/babel/messages/catalog.py
@@ -19,11 +19,11 @@
 from copy import copy
 
 from babel import __version__ as VERSION
-from babel.core import Locale
+from babel.core import Locale, UnknownLocaleError
 from babel.dates import format_datetime
 from babel.messages.plurals import get_plural
 from babel.util import odict, distinct, LOCALTZ, FixedOffsetTimezone
-from babel._compat import string_types, number_types, PY2, cmp
+from babel._compat import string_types, number_types, PY2, cmp, text_type
 
 __all__ = ['Message', 'Catalog', 'TranslationError']
 
@@ -267,8 +267,6 @@ def __init__(self, locale=None, domain=None, header_comment=DEFAULT_HEADER,
         :param fuzzy: the fuzzy bit on the catalog header
         """
         self.domain = domain
-        if locale:
-            locale = Locale.parse(locale)
         self.locale = locale
         self._header_comment = header_comment
         self._messages = odict()
@@ -301,6 +299,36 @@ def __init__(self, locale=None, domain=None, header_comment=DEFAULT_HEADER,
         self._num_plurals = None
         self._plural_expr = None
 
+    def _set_locale(self, locale):
+        if locale is None:
+            self._locale_identifier = None
+            self._locale = None
+            return
+
+        if isinstance(locale, Locale):
+            self._locale_identifier = text_type(locale)
+            self._locale = locale
+            return
+
+        if isinstance(locale, string_types):
+            self._locale_identifier = text_type(locale)
+            try:
+                self._locale = Locale.parse(locale)
+            except UnknownLocaleError:
+                self._locale = None
+            return
+
+        raise TypeError('`locale` must be a Locale, a locale identifier string, or None; got %r' % locale)
+
+    def _get_locale(self):
+        return self._locale
+
+    def _get_locale_identifier(self):
+        return self._locale_identifier
+
+    locale = property(_get_locale, _set_locale)
+    locale_identifier = property(_get_locale_identifier)
+
     def _get_header_comment(self):
         comment = self._header_comment
         year = datetime.now(LOCALTZ).strftime('%Y')
@@ -310,9 +338,9 @@ def _get_header_comment(self):
                          .replace('VERSION', self.version) \
                          .replace('YEAR', year) \
                          .replace('ORGANIZATION', self.copyright_holder)
-        if self.locale:
-            comment = comment.replace('Translations template', '%s translations'
-                                      % self.locale.english_name)
+        locale_name = (self.locale.english_name if self.locale else self.locale_identifier)
+        if locale_name:
+            comment = comment.replace('Translations template', '%s translations' % locale_name)
         return comment
 
     def _set_header_comment(self, string):
@@ -366,12 +394,12 @@ def _get_mime_headers(self):
         else:
             headers.append(('PO-Revision-Date', self.revision_date))
         headers.append(('Last-Translator', self.last_translator))
-        if self.locale is not None:
-            headers.append(('Language', str(self.locale)))
-        if (self.locale is not None) and ('LANGUAGE' in self.language_team):
+        if self.locale_identifier:
+            headers.append(('Language', str(self.locale_identifier)))
+        if self.locale_identifier and ('LANGUAGE' in self.language_team):
             headers.append(('Language-Team',
                             self.language_team.replace('LANGUAGE',
-                                                       str(self.locale))))
+                                                       str(self.locale_identifier))))
         else:
             headers.append(('Language-Team', self.language_team))
         if self.locale is not None:
@@ -396,7 +424,7 @@ def _set_mime_headers(self, headers):
                 self.last_translator = value
             elif name == 'language':
                 value = value.replace('-', '_')
-                self.locale = Locale.parse(value)
+                self._set_locale(value)
             elif name == 'language-team':
                 self.language_team = value
             elif name == 'content-type':
@@ -490,6 +518,8 @@ def plural_expr(self):
         '(n != 1)'
         >>> Catalog(locale='ga').plural_expr
         '(n==1 ? 0 : n==2 ? 1 : n>=3 && n<=6 ? 2 : n>=7 && n<=10 ? 3 : 4)'
+        >>> Catalog(locale='ding').plural_expr  # unknown locale
+        '(n != 1)'
 
         :type: `string_types`"""
         if self._plural_expr is None:
diff --git a/tests/messages/test_pofile.py b/tests/messages/test_pofile.py
index 002954f8a..b2c6f6702 100644
--- a/tests/messages/test_pofile.py
+++ b/tests/messages/test_pofile.py
@@ -494,6 +494,7 @@ def test_invalid_pofile_with_abort_flag(self):
         with self.assertRaises(pofile.PoFileError) as e:
             parser._invalid_pofile(line, lineno, msg)
 
+
 class WritePoTestCase(unittest.TestCase):
 
     def test_join_locations(self):
@@ -864,3 +865,25 @@ def test_denormalize_on_msgstr_without_empty_first_line(self):
         self.assertEqual(expected_denormalized, pofile.denormalize(msgstr))
         self.assertEqual(expected_denormalized,
                          pofile.denormalize('""\n' + msgstr))
+
+
+def test_unknown_language_roundtrip():
+    buf = StringIO(r'''
+msgid ""
+msgstr ""
+"Language: sr_SP\n"''')
+    catalog = pofile.read_po(buf)
+    assert catalog.locale_identifier == 'sr_SP'
+    assert not catalog.locale
+    buf = BytesIO()
+    pofile.write_po(buf, catalog)
+    assert 'sr_SP' in buf.getvalue().decode()
+
+
+def test_unknown_language_write():
+    catalog = Catalog(locale='sr_SP')
+    assert catalog.locale_identifier == 'sr_SP'
+    assert not catalog.locale
+    buf = BytesIO()
+    pofile.write_po(buf, catalog)
+    assert 'sr_SP' in buf.getvalue().decode()