Fixed: Mul file not recognized as such and listing pretty much all la…

…nguages.

* ZIM files that have multiple languages are represented as a single string with comma-separated values (e.g., "eng,fra,vie,ita,ara,por"). We have modified the code to check for these cases and ensure that any ZIM file containing more than one language is shown under the "Multiple languages" section.

core/src/main/java/org/kiwix/kiwixmobile/core/data/Repository.kt

@@ -68,8 +68,22 @@ class Repository @Inject internal constructor(
       .observeOn(mainThread)
 
   override fun booksOnDiskAsListItems(): Flowable<List<BooksOnDiskListItem>> = bookDao.books()
-    .map { it.sortedBy { bookOnDisk -> bookOnDisk.book.language + bookOnDisk.book.title } }
     .map {
+      it.map { bookOnDisk ->
+        // If the book contains more than one language, it comes in a single string with commas.
+        // e.g., "eng,fra,vie,ita,ara,por". Check if the language contains a comma,
+        // then move this book to the "Multiple languages" section.
+        if (bookOnDisk.book.language.contains(',')) {
+          bookOnDisk.copy().apply {
+            // Set the language to "mul" for the book so that it is shown
+            // in the "Multiple languages" section.
+            book.language = "mul"
+          }
+        } else {
+          bookOnDisk
+        }
+      }.sortedBy { bookOnDisk -> bookOnDisk.book.language + bookOnDisk.book.title }
+    }.map {
       HeaderizableList<BooksOnDiskListItem, BookOnDisk, LanguageItem>(it).foldOverAddingHeaders(
         { bookOnDisk -> LanguageItem(bookOnDisk.locale) },
         { current, next -> current.locale.displayName != next.locale.displayName }