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

Symptoms

• When opening Plesk interface, it fails to load with the message:

  PLESK_INFO: Server Error
  500
  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 when running the command:

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

Cause

Corrupted locale files.

Resolution

1. Connect to your Plesk server via RDP.

2. Download the latest version of locale packages:

   2.1. Open Plesk for Windows repository.

   2.2. Open the directory PLESK_WIN_XX_X_XX where XX_X_XX is the latest available Plesk version

   2.3. Open dist-windows/ directory.

   2.4. Download the locale packages plesk-locale-base-en-US.zip and plesk-l10n.zip.

3. For safety reasons, create a copy of folders %plesk_dir%admin\application\ and %plesk_dir%admin\plib\.

4. Open downloaded zip file plesk-locale-base-en-US.zip and:

   4.1. Copy application\ folder and paste it in %plesk_dir%admin\.

   4.2. Copy the plib\ folder and paste it in %plesk_dir%admin\.

   Note: Replace the files in destination, if asked.

5. Open downloaded zip file plesk-l10n.zip and:

   5.1. Copy application\ folder and paste it in %plesk_dir%admin\.

   5.2. Copy the plib\ folder and paste it in %plesk_dir%admin\.

   Note: Replace the files in destination, if asked.

6. Start a command prompt as an Administrator.

7. Re-register locales in Plesk:

   C:\> plesk php "C:\Program Files (x86)\Plesk\admin\plib\scripts\add-locales.php"

8. Install any missing packages using Plesk Installer:

   C:\> plesk installer update