Content server: Fix changing the language of a book not working for non-English user interface language and for books that have no existing language. Fixes #2085005 [Calibre server fails updating book with Spanish characters](https://bugs.launchpad.net/calibre/+bug/2085005)

src/calibre/srv/cdb.py

@@ -17,6 +17,7 @@ from calibre.srv.metadata import book_as_json
 from calibre.srv.routes import endpoint, json, msgpack_or_json
 from calibre.srv.utils import get_db, get_library_data
 from calibre.utils.imghdr import what
+from calibre.utils.localization import canonicalize_lang, reverse_lang_map_for_ui
 from calibre.utils.serialize import MSGPACK_MIME, json_loads, msgpack_loads
 from calibre.utils.speedups import ReadOnlyFileBuffer
 from polyglot.binary import from_base64_bytes
@@ -206,6 +207,11 @@ def cdb_set_fields(ctx, rd, book_id, library_id):
         dirtied.add(book_id)
 
     for field, value in iteritems(changes):
+        if field == 'languages' and value:
+            rmap = reverse_lang_map_for_ui()
+            def to_lang_code(x):
+                return rmap.get(x, canonicalize_lang(x))
+            value = list(filter(None, map(to_lang_code, value)))
         dirtied |= db.set_field(field, {book_id: value})
     ctx.notify_changes(db.backend.library_path, metadata(dirtied))
     all_ids = dirtied if all_dirtied else (dirtied & loaded_book_ids)

src/calibre/utils/localization.py

@@ -505,6 +505,13 @@ def lang_map_for_ui():
     return ans
 
 
+def reverse_lang_map_for_ui():
+    ans = getattr(reverse_lang_map_for_ui, 'ans', None)
+    if ans is None:
+        ans = reverse_lang_map_for_ui.ans = {v: k for k, v in lang_map_for_ui().items()}
+    return ans
+
+
 def langnames_to_langcodes(names):
     '''
     Given a list of localized language names return a mapping of the names to 3

src/pyj/book_list/edit_metadata.pyj

@@ -367,7 +367,8 @@ def multiple_line_edit(list_to_ui, ui_to_list, container_id, book_id, field, fm,
     )
     val = (resolved_metadata(mi, field) or v'[]')
     if field is 'languages':
-        val = [mi.lang_names[l] or l for l in val]
+        ln = mi.lang_names or {}
+        val = [ln[l] or l for l in val]
     if list_to_ui:
         val = val.join(list_to_ui)
     le.value = val