Fixed: Check language of book file matches edition language if possible

src/NzbDrone.Core/MediaFiles/BookImport/Identification/Distance.cs

@@ -21,6 +21,7 @@ namespace NzbDrone.Core.MediaFiles.BookImport.Identification
             { "media_format", 1.0 },
             { "year", 1.0 },
             { "country", 0.5 },
+            { "language", 5.0 },
             { "label", 0.5 },
             { "catalog_number", 0.5 },
             { "book_disambiguation", 0.5 },

src/NzbDrone.Core/MediaFiles/BookImport/Identification/DistanceCalculator.cs

@@ -6,6 +6,7 @@ using NLog;
 using NzbDrone.Common.Extensions;
 using NzbDrone.Common.Instrumentation;
 using NzbDrone.Core.Books;
+using NzbDrone.Core.Books.Calibre;
 using NzbDrone.Core.Parser;
 using NzbDrone.Core.Parser.Model;
 
@@ -113,6 +114,15 @@ namespace NzbDrone.Core.MediaFiles.BookImport.Identification
                 Logger.Trace($"year: {localYear} vs {edition.ReleaseDate?.Year}; {dist.NormalizedDistance()}");
             }
 
+            // Language - only if set for both the local book and remote edition
+            var localLanguage = localTracks.MostCommon(x => x.FileTrackInfo.Language).CanonicalizeLanguage();
+            var editionLanguage = edition.Language.CanonicalizeLanguage();
+            if (localLanguage.IsNotNullOrWhiteSpace() && editionLanguage.IsNotNullOrWhiteSpace())
+            {
+                dist.AddBool("language", localLanguage != editionLanguage);
+                Logger.Trace($"language: {localLanguage} vs {editionLanguage}; {dist.NormalizedDistance()}");
+            }
+
             return dist;
         }