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 login to Plesk with the error:

  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 output in Command Prompt commands, e.g:

  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:

   2.1. Select the directory of the latest Plesk version listed.
   2.2. Open the dist-windows/ directory and download the locale file.

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

4. Create a temporary directory for the extraction of the package (e.g.: C:locales)

5. Open the Command Prompt and extract the downloaded package into the temporary directory using the following commands:

   cd C:UsersAdministratorDownloads

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

   Note: Replace the download and extraction temporary paths accordingly if differs from the above ones.

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 running the following CMD command:

   plesk installer update