diff --git a/README.md b/README.md
index 7099bbbe..f561c840 100644
--- a/README.md
+++ b/README.md
@@ -1,4 +1,4 @@
-[![Download the latest release](docs/img/download-button.png)](https://github.com/peter88213/novelibre/raw/main/dist/novelibre_v4.15.3.pyzw)
+[![Download the latest release](docs/img/download-button.png)](https://github.com/peter88213/novelibre/raw/main/dist/novelibre_v4.15.4.pyzw)
 [![Changelog](docs/img/changelog-button.png)](docs/changelog.md)
 [![News](docs/img/news-button.png)](https://github.com/peter88213/novelibre/discussions/1)
 [![Online help](docs/img/help-button.png)](https://peter88213.github.io/nvhelp-en/)
@@ -82,10 +82,10 @@ I use the program myself and fix bugs immediately if I notice any. As far as I c
 
 ### Default: Executable Python zip archive
 
-Download the latest release [novelibre_v4.15.3.pyzw](https://github.com/peter88213/novelibre/raw/main/dist/novelibre_v4.15.3.pyzw)
+Download the latest release [novelibre_v4.15.4.pyzw](https://github.com/peter88213/novelibre/raw/main/dist/novelibre_v4.15.4.pyzw)
 
-- Launch *novelibre_v4.15.3.pyzw* by double-clicking (Windows/Linux desktop),
-- or execute `python novelibre_v4.15.3.pyzw` (Windows), resp. `python3 novelibre_v4.15.3.pyzw` (Linux) on the command line.
+- Launch *novelibre_v4.15.4.pyzw* by double-clicking (Windows/Linux desktop),
+- or execute `python novelibre_v4.15.4.pyzw` (Windows), resp. `python3 novelibre_v4.15.4.pyzw` (Linux) on the command line.
 
 #### Important
 
@@ -101,9 +101,9 @@ the zip file.
 
 ### Alternative: Zip file
 
-The package is also available in zip format: [novelibre_v4.15.3.zip](https://github.com/peter88213/novelibre/raw/main/dist/novelibre_v4.15.3.zip)
+The package is also available in zip format: [novelibre_v4.15.4.zip](https://github.com/peter88213/novelibre/raw/main/dist/novelibre_v4.15.4.zip)
 
-- Extract the *novelibre_v4.15.3* folder from the downloaded zipfile "novelibre_v4.15.3.zip".
+- Extract the *novelibre_v4.15.4* folder from the downloaded zipfile "novelibre_v4.15.4.zip".
 - Move into this new folder and launch *setup.pyw* by double-clicking (Windows/Linux desktop), 
 - or execute `python setup.pyw` (Windows), resp. `python3 setup.pyw` (Linux) on the command line.
 
diff --git a/VERSION b/VERSION
index 2bfad2a9..b89666f7 100644
--- a/VERSION
+++ b/VERSION
@@ -1,3 +1,3 @@
 [LATEST]
-version = 4.15.3
-download_link = https://github.com/peter88213/novelibre/raw/main/dist/novelibre_v4.15.3.pyzw
+version = 4.15.4
+download_link = https://github.com/peter88213/novelibre/raw/main/dist/novelibre_v4.15.4.pyzw
diff --git a/dist/novelibre_v4.15.3.pyzw b/dist/novelibre_v4.15.4.pyzw
similarity index 53%
rename from dist/novelibre_v4.15.3.pyzw
rename to dist/novelibre_v4.15.4.pyzw
index bac8302a..6e70fa09 100644
Binary files a/dist/novelibre_v4.15.3.pyzw and b/dist/novelibre_v4.15.4.pyzw differ
diff --git a/dist/novelibre_v4.15.3.zip b/dist/novelibre_v4.15.4.zip
similarity index 52%
rename from dist/novelibre_v4.15.3.zip
rename to dist/novelibre_v4.15.4.zip
index c3e3928a..ec822805 100644
Binary files a/dist/novelibre_v4.15.3.zip and b/dist/novelibre_v4.15.4.zip differ
diff --git a/docs/changelog.md b/docs/changelog.md
index 7b8ebb74..4ad95057 100644
--- a/docs/changelog.md
+++ b/docs/changelog.md
@@ -8,6 +8,14 @@
 
 See the [GitHub "Features" project](https://github.com/users/peter88213/projects/14).
 
+### Version 4.15.4
+
+Refactor the code for better maintainability
+
+- Remove the isLocked property from the NvController class.
+
+Based on novxlib 4.8.0
+Based on apptk 2.2.0
 
 ### Version 4.15.3
 
diff --git a/i18n/de.po b/i18n/de.po
index 2477eff5..34b327a4 100644
--- a/i18n/de.po
+++ b/i18n/de.po
@@ -3,9 +3,9 @@
 #
 msgid ""
 msgstr ""
-"Project-Id-Version: 4.15.3\n"
-"POT-Creation-Date: 2024-10-31 08:04:10\n"
-"PO-Revision-Date: 2024-10-31 08:04:10\n"
+"Project-Id-Version: 4.15.4\n"
+"POT-Creation-Date: 2024-10-31 19:54:08\n"
+"PO-Revision-Date: 2024-10-31 19:54:08\n"
 "Last-Translator: Peter Triesberger\n"
 "Language: de\n"
 "MIME-Version: 1.0\n"
diff --git a/i18n/locale/de/LC_MESSAGES/novelibre.mo b/i18n/locale/de/LC_MESSAGES/novelibre.mo
index 334ab668..852ba661 100644
Binary files a/i18n/locale/de/LC_MESSAGES/novelibre.mo and b/i18n/locale/de/LC_MESSAGES/novelibre.mo differ
diff --git a/i18n/messages.pot b/i18n/messages.pot
index 33c6d0e3..69b7bfeb 100644
--- a/i18n/messages.pot
+++ b/i18n/messages.pot
@@ -3,8 +3,8 @@
 #
 msgid ""
 msgstr ""
-"Project-Id-Version: 4.15.3\n"
-"POT-Creation-Date: 2024-10-31 08:04:10\n"
+"Project-Id-Version: 4.15.4\n"
+"POT-Creation-Date: 2024-10-31 19:54:08\n"
 "PO-Revision-Date: YEAR-MO-DA HO:MI+ZONE\n"
 "Last-Translator: FULL NAME <EMAIL@ADDRESS>\n"
 "Language: LANGUAGE\n"
diff --git a/src/nvlib/controller/nv_controller.py b/src/nvlib/controller/nv_controller.py
index 95d4814f..d15f5bc0 100644
--- a/src/nvlib/controller/nv_controller.py
+++ b/src/nvlib/controller/nv_controller.py
@@ -88,15 +88,6 @@ def __init__(self, title, tempDir):
 
         self._ui.tv.reset_view()
 
-    @property
-    def isLocked(self):
-        # Boolean -- True if a lock file exists for the current project.
-        return self._internalLockFlag
-
-    @isLocked.setter
-    def isLocked(self, setFlag):
-        raise NotImplementedError
-
     def add_chapter(self, **kwargs):
         """Add a chapter to the novel.
              
diff --git a/tools/build.py b/tools/build.py
index 6092581a..2302ecd7 100644
--- a/tools/build.py
+++ b/tools/build.py
@@ -12,7 +12,7 @@
 sys.path.insert(0, f'{os.getcwd()}/../../novelibre/tools')
 from package_builder import PackageBuilder
 
-VERSION = '4.15.3'
+VERSION = '4.15.4'
 
 
 class ApplicationBuilder(PackageBuilder):