diff --git a/src/calibre/db/cache.py b/src/calibre/db/cache.py
index 7bed56dc5e..31c7db915b 100644
--- a/src/calibre/db/cache.py
+++ b/src/calibre/db/cache.py
@@ -35,6 +35,7 @@ from calibre.ptempfile import (base_dir, PersistentTemporaryFile,
 from calibre.utils.config import prefs, tweaks
 from calibre.utils.date import now as nowf, utcnow, UNDEFINED_DATE
 from calibre.utils.icu import sort_key
+from calibre.utils.localization import canonicalize_lang
 
 
 def api(f):
@@ -1952,6 +1953,7 @@ class Cache(object):
         title (title is fuzzy matched). See also :meth:`data_for_find_identical_books`. '''
         from calibre.db.utils import fuzzy_title
         identical_book_ids = set()
+        langq = tuple(filter(lambda x: x and x != 'und', map(canonicalize_lang, mi.languages or ())))
         if mi.authors:
             try:
                 quathors = mi.authors[:20]  # Too many authors causes parsing of the search expression to fail
@@ -1980,7 +1982,9 @@ class Cache(object):
                 fbook_title = fuzzy_title(fbook_title)
                 mbook_title = fuzzy_title(mi.title)
                 if fbook_title == mbook_title:
-                    identical_book_ids.add(book_id)
+                    bl = self._field_for('languages', book_id)
+                    if not langq or not bl or bl == langq:
+                        identical_book_ids.add(book_id)
         return identical_book_ids
 
     @read_api
diff --git a/src/calibre/db/tests/reading.py b/src/calibre/db/tests/reading.py
index 34435a7360..1ef4441c70 100644
--- a/src/calibre/db/tests/reading.py
+++ b/src/calibre/db/tests/reading.py
@@ -684,11 +684,17 @@ class ReadingTest(BaseTest):
         from calibre.db.utils import find_identical_books
         # 'find_identical_books': [(,), (Metadata('unknown'),), (Metadata('xxxx'),)],
         cache = self.init_cache(self.library_path)
+        cache.set_field('languages', {1: ('fra', 'deu')})
         data = cache.data_for_find_identical_books()
+        lm = cache.get_metadata(1)
+        lm2 = cache.get_metadata(1)
+        lm2.languages = ['eng']
         for mi, books in (
                 (Metadata('title one', ['author one']), {2}),
                 (Metadata(_('Unknown')), {3}),
                 (Metadata('title two', ['author one']), {1}),
+                (lm, {1}),
+                (lm2, set()),
         ):
             self.assertEqual(books, cache.find_identical_books(mi))
             self.assertEqual(books, find_identical_books(mi, data))
diff --git a/src/calibre/db/utils.py b/src/calibre/db/utils.py
index 4f102aa31e..7e1738afc6 100644
--- a/src/calibre/db/utils.py
+++ b/src/calibre/db/utils.py
@@ -34,6 +34,7 @@ def force_to_bool(val):
             val = None
     return val
 
+
 _fuzzy_title_patterns = None
 
 
@@ -82,22 +83,15 @@ def find_identical_books(mi, data):
         if fuzzy_title(title) == titleq:
             ans.add(book_id)
 
-    if ans is None:
-        return set()
-
-    alg = set()
-    langq = canonicalize_lang(mi.language)
-    if langq is None:
+    langq = tuple(filter(lambda x: x and x != 'und', map(canonicalize_lang, mi.languages or ())))
+    if not langq:
         return ans
-    for book_id in ans:
-        lang_list = lang_map.get(book_id, '')
-        if lang_list is None:
-            return ans
-        for lang in lang_list:
-            lang=canonicalize_lang(lang)
-            if lang == langq:
-                alg.add(book_id)
-    return alg
+
+    def lang_matches(book_id):
+        book_langq = lang_map.get(book_id)
+        return not book_langq or langq == book_langq
+
+    return {book_id for book_id in ans if lang_matches(book_id)}
 
 
 Entry = namedtuple('Entry', 'path size timestamp thumbnail_size')
@@ -383,6 +377,7 @@ class ThumbnailCache(object):
             if hasattr(self, 'total_size'):
                 self._apply_size()
 
+
 number_separators = None
 
 
diff --git a/src/calibre/gui2/actions/copy_to_library.py b/src/calibre/gui2/actions/copy_to_library.py
index aca0c76b9e..ff264b00f9 100644
--- a/src/calibre/gui2/actions/copy_to_library.py
+++ b/src/calibre/gui2/actions/copy_to_library.py
@@ -351,7 +351,7 @@ class DuplicatesQuestion(QDialog):  # {{{
         QDialog.__init__(self, parent)
         l = QVBoxLayout()
         self.setLayout(l)
-        self.la = la = QLabel(_('Books with the same, language, title and author as the following already exist in the library %s.'
+        self.la = la = QLabel(_('Books with the same, title, author and language as the following already exist in the library %s.'
                                 ' Select which books you want copied anyway.') %
                               os.path.basename(loc))
         la.setWordWrap(True)
diff --git a/src/calibre/gui2/preferences/adding.ui b/src/calibre/gui2/preferences/adding.ui
index bb42c68132..5eb2ccfbfe 100644
--- a/src/calibre/gui2/preferences/adding.ui
+++ b/src/calibre/gui2/preferences/adding.ui
@@ -111,7 +111,7 @@
        <item row="3" column="0" colspan="2">
         <widget class="QCheckBox" name="opt_check_for_dupes_on_ctl">
          <property name="text">
-          <string>When using the &quot;Copy to library&quot; action check for &amp;duplicates with the same language, title, and author</string>
+          <string>When using the &quot;Copy to library&quot; action check for &amp;duplicates with the same title, author and language</string>
          </property>
         </widget>
        </item>