When checking added books for duplicates, also check on the language

field. So books with the same title/authors but different languages are
not considered duplicates.

src/calibre/db/cache.py

@@ -1931,12 +1931,13 @@ class Cache(object):
         author_map = defaultdict(set)
         for aid, author in at.id_map.iteritems():
             author_map[icu_lower(author)].add(aid)
-        return (author_map, at.col_book_map.copy(), self.fields['title'].table.book_col_map.copy())
+        return (author_map, at.col_book_map.copy(), self.fields['title'].table.book_col_map.copy(), self.fields['languages'].book_value_map.copy())
 
     @read_api
     def update_data_for_find_identical_books(self, book_id, data):
-        author_map, author_book_map, title_map = data
+        author_map, author_book_map, title_map, lang_map = data
         title_map[book_id] = self._field_for('title', book_id)
+        lang_map[book_id] = self._field_for('languages', book_id)
         at = self.fields['authors'].table
         for aid in at.book_col_map.get(book_id, ()):
             author_map[icu_lower(at.id_map[aid])].add(aid)

src/calibre/db/utils.py

@@ -15,6 +15,8 @@ from threading import Lock
 from calibre import as_unicode, prints
 from calibre.constants import cache_dir, get_windows_number_formats, iswindows
 
+from calibre.utils.localization import canonicalize_lang
+
 
 def force_to_bool(val):
     if isinstance(val, (str, unicode)):
@@ -59,7 +61,7 @@ def fuzzy_title(title):
 
 
 def find_identical_books(mi, data):
-    author_map, aid_map, title_map = data
+    author_map, aid_map, title_map, lang_map = data
     found_books = None
     for a in mi.authors:
         author_ids = author_map.get(icu_lower(a))
@@ -79,7 +81,23 @@ def find_identical_books(mi, data):
         title = title_map.get(book_id, '')
         if fuzzy_title(title) == titleq:
             ans.add(book_id)
-    return ans
+
+    if ans is None:
+        return set()
+
+    alg = set()
+    langq = canonicalize_lang(mi.language)
+    if langq is None:
+        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
 
 
 Entry = namedtuple('Entry', 'path size timestamp thumbnail_size')

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 title and author as the following already exist in the library %s.'
+        self.la = la = QLabel(_('Books with the same, language, title and author as the following already exist in the library %s.'
                                 ' Select which books you want copied anyway.') %
                               os.path.basename(loc))
         la.setWordWrap(True)

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 title and author</string>
+          <string>When using the &quot;Copy to library&quot; action check for &amp;duplicates with the same language, title, and author</string>
          </property>
         </widget>
        </item>