Resolve "Weekdays not translated"

Closes #655 (closed)

docs/admin/10_install.rst

@@ -34,6 +34,7 @@ For an installation on a dedicated server, the following prerequisites are neede
  * nginx
  * Python 3.9
  * Some system dependencies to build Python modules and manage frontend files
+ * System locales for all supported languages
  * The aforementioned paths
 
 Install system packages
@@ -53,7 +54,8 @@ Install some packages from the Debian package system.
                python3-virtualenv \
                chromium \
                redis-server \
-               postgresql
+               postgresql \
+               locales-all
 
 Create PostgreSQL user and database
 ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~