diff --git a/src/calibre/gui2/viewer/web_view.py b/src/calibre/gui2/viewer/web_view.py
index 219e574122..c98065a558 100644
--- a/src/calibre/gui2/viewer/web_view.py
+++ b/src/calibre/gui2/viewer/web_view.py
@@ -26,6 +26,7 @@ from calibre.gui2.webengine import (
     Bridge, RestartingWebEngineView, create_script, from_js, insert_scripts,
     secure_webengine, to_js
 )
+from calibre.srv.code import get_translations_data
 from calibre.utils.config import JSONConfig
 from polyglot.builtins import iteritems
 
@@ -155,6 +156,9 @@ def create_profile():
             from calibre.utils.rapydscript import compile_viewer
             compile_viewer()
         js = P('viewer.js', data=True, allow_user_override=False)
+        translations_json = get_translations_data()
+        if translations_json:
+            js = (b'window.calibre_translations_data = %s;\n\n' % translations_json) + js
         insert_scripts(ans, create_script('viewer.js', js))
         url_handler = UrlSchemeHandler(ans)
         ans.installUrlSchemeHandler(QByteArray(FAKE_PROTOCOL.encode('ascii')), url_handler)
diff --git a/src/calibre/srv/code.py b/src/calibre/srv/code.py
index ce41b7d122..b87c017931 100644
--- a/src/calibre/srv/code.py
+++ b/src/calibre/srv/code.py
@@ -9,7 +9,7 @@ import random
 import shutil
 import sys
 import zipfile
-from json import load as load_json_file
+from json import load as load_json_file, loads as json_loads
 from threading import Lock
 
 from calibre import as_unicode
@@ -95,25 +95,27 @@ def get_basic_query_data(ctx, rd):
     return library_id, db, sorts, orders, rd.query.get('vl') or ''
 
 
-_cached_translations = None
+def get_translations_data():
+    with zipfile.ZipFile(
+        P('content-server/locales.zip', allow_user_override=False), 'r'
+    ) as zf:
+        names = set(zf.namelist())
+        lang = get_lang()
+        if lang not in names:
+            xlang = lang.split('_')[0].lower()
+            if xlang in names:
+                lang = xlang
+        if lang in names:
+            return zf.open(lang, 'r').read()
 
 
 def get_translations():
-    global _cached_translations
-    if _cached_translations is None:
-        _cached_translations = False
-        with zipfile.ZipFile(
-            P('content-server/locales.zip', allow_user_override=False), 'r'
-        ) as zf:
-            names = set(zf.namelist())
-            lang = get_lang()
-            if lang not in names:
-                xlang = lang.split('_')[0].lower()
-                if xlang in names:
-                    lang = xlang
-            if lang in names:
-                _cached_translations = load_json_file(zf.open(lang, 'r'))
-    return _cached_translations
+    if not hasattr(get_translations, 'cached'):
+        get_translations.cached = False
+        data = get_translations_data()
+        if data:
+            get_translations.cached = json_loads(data)
+    return get_translations.cached
 
 
 def custom_list_template():
diff --git a/src/pyj/viewer-main.pyj b/src/pyj/viewer-main.pyj
index 8af6a76639..8e6104ff1c 100644
--- a/src/pyj/viewer-main.pyj
+++ b/src/pyj/viewer-main.pyj
@@ -4,7 +4,7 @@ from __python__ import bound_methods, hash_literals
 
 import traceback
 from elementmaker import E
-from gettext import gettext as _
+from gettext import gettext as _, install
 
 import initialize  # noqa: unused-import
 from ajax import ajax
@@ -238,6 +238,8 @@ def update_font_size():
 
 if window is window.top:
     # main
+    if window.calibre_translations_data:
+        install(window.calibre_translations_data)
     ui_operations.get_file = get_file
     ui_operations.get_mathjax_files = get_mathjax_files
     ui_operations.update_url_state = update_url_state
@@ -262,3 +264,4 @@ if window is window.top:
 else:
     # iframe
     iframe_main()
+window.calibre_translations_data = v'undefined'