diff --git a/pelican/generators.py b/pelican/generators.py
index 1b584d3f..7a616759 100644
--- a/pelican/generators.py
+++ b/pelican/generators.py
@@ -309,6 +309,8 @@ class ArticlesGenerator(Generator):
                 # format string syntax can be used for specifying the
                 # period archive dates
                 date = archive[0].date
+                category = archive[0].category
+                lang = archive[0].lang
                 # Under python 2, with non-ascii locales, u"{:%b}".format(date) might raise UnicodeDecodeError
                 # because u"{:%b}".format(date) will call date.__format__(u"%b"), which will return a byte string
                 # and not a unicode string.
@@ -316,12 +318,20 @@ class ArticlesGenerator(Generator):
                 # locale.setlocale(locale.LC_ALL, 'ja_JP.utf8')
                 # date.__format__(u"%b") == '12\xe6\x9c\x88' # True
                 try:
-                    save_as = save_as_fmt.format(date=date)
+                    save_as = save_as_fmt.format(
+                        date=date,
+                        category=category,
+                        lang=lang
+                    )
                 except UnicodeDecodeError:
                     # Python2 only:
                     # Let date.__format__() work with byte strings instead of characters since it fails to work with characters
                     bytes_save_as_fmt = save_as_fmt.encode('utf8')
-                    bytes_save_as     = bytes_save_as_fmt.format(date=date)
+                    bytes_save_as     = bytes_save_as_fmt.format(
+                        date=date,
+                        category=category,
+                        lang=lang
+                    )
                     save_as           = unicode(bytes_save_as,'utf8')
                 context = self.context.copy()