Unable to log in to Plesk: 500 Session_exception. Unable to set up default locale: default locale does not exist or undefined

Symptoms

• Unable to log in to Plesk:

  Server Error
  500
  Session_Exception
  Unable to set up default locale: default locale does not exist or undefined.
  Type Session_Exception
  Message Unable to set up default locale: default locale does not exist or undefined.
  File Panel.php
  Line 72

• Variable names are shown instead of human-readable words/sentences in Command Prompt commands output. For example:

  C:> plesk bin server_pref --locales-list
  cu_servpref__locales_available

Cause

Corrupted locale files.

Resolution

1. Connect to the server via RDP.

2. Download the latest version of package plesk-locale-base-en-US.msi from the Windows repository https://autoinstall-win.plesk.com/pool/release/:

   1. Select the last directory in the list - that would be the latest Plesk version
   2. Open the dist-windows/ directory

3. Make a backup of %plesk_dir%adminapplication and %plesk_dir%adminplib directories.

4. Create a temporary directory for extracting the plesk-locale-base-en-US.msi package (for example, C:locales)

5. Open the Command Prompt and extract the package files to a temporary directory using the following commands:

   Note: this example assumes that the package has been downloaded to C:UsersAdministratorDownloads. Replace it with the actual package's path if the download location was different

   C:> cd C:UsersAdministratorDownloads

   C:>msiexec /a "plesk-locale-base-en-US.msi" /qb targetdir=C:locales

6. Copy the extracted files and directories from C:locales to %plesk_dir%adminapplication and %plesk_dir%adminplib, replacing old data.

7. Reinstall any missing Plesk components:

   C:>plesk installer update