Steps to reproduce
- Update to 10.0.5.4
 - Change some settings like cron (instead of Ajax) and enable file locking
 - Restart server
 - Try to go to the GENERAL administration pannel
 
Expected behaviour
The administration panel
Actual behaviour
Empty page with only Cron displayed. Page code is like that (< are [ and > are ]):
[div class=“section” id=“backgroundjobs”]
[h2 class=“app-name has-documentation”>Cron[/h2]
[p class=“cronlog inlineblock”]
And I’ve got an error in Apche2 log specific to that page loading process:
[Wed Jan 24 18:55:16.931955 2018] [:error] [pid 20626] [client 127.0.0.1:35464] PHP Fatal error: Method OC_L10N_String::__toString() must not throw an exception, caught Error: Class ‘Symfony\Component\Translation\PluralizationRules’ not found in /home/www/owncloud/lib/private/L10N/L10N.php on line 0
Server configuration
Operating system: Ubuntu 17.10 (I know you’re not compatible for it but I’ve the same error on 17.4 just before dist-upgrade)
Web server: Apache/2.4.27
Database: mysql Ver 14.14 Distrib 5.7.21
PHP version: PHP 7.1.11
ownCloud version: 10.0.5.4
Updated from an older ownCloud or fresh install: Updated from 9.something (don’t remimber which version)
Where did you install ownCloud from: Official repo for Ubuntu from owncloud docs
Signing status (ownCloud 9.0 and above): No errors have been found.
The content of config/config.php:
{
    "system": {
        "passwordsalt": "***REMOVED SENSITIVE VALUE***",
        "secret": "***REMOVED SENSITIVE VALUE***",
        "trusted_domains": [
            "***REMOVED SENSITIVE VALUE***",
            "***REMOVED SENSITIVE VALUE***"
        ],
        "forcessl": true,
        "instanceid": "oc7bd28573e8",
        "datadirectory": "\/var\/www\/owncloud\/data",
        "overwrite.cli.url": "***REMOVED SENSITIVE VALUE***",
        "dbtype": "mysql",
        "version": "10.0.5.4",
        "dbname": "owncloud",
        "dbhost": "localhost",
        "dbtableprefix": "oc_",
        "dbuser": "***REMOVED SENSITIVE VALUE***",
        "dbpassword": "***REMOVED SENSITIVE VALUE***",
        "installed": true,
        "mail_from_address": "***REMOVED SENSITIVE VALUE***",
        "mail_smtpmode": "php",
        "mail_domain": "***REMOVED SENSITIVE VALUE***",
        "maintenance": false,
        "loglevel": "2",
        "memcache.locking": "\\OC\\Memcache\\Redis",
        "redis": {
            "host": "localhost",
            "port": 6379
        },
        "enable_previews": true,
        "updatechecker": false,
        "theme": ""
    }
}
List of activated apps:
Enabled:
  - activity: 2.3.6
  - announcementcenter: 1.2.0
  - audioplayer: 2.2.4
  - comments: 0.3.0
  - configreport: 0.1.1
  - dav: 0.3.2
  - encryption: 1.3.1
  - federatedfilesharing: 0.3.1
  - files: 1.5.1
  - files_external: 0.7.1
  - files_pdfviewer: 0.8.2
  - files_sharing: 0.10.1
  - files_texteditor: 2.2.1
  - files_trashbin: 0.9.1
  - files_versions: 1.3.0
  - files_videoplayer: 0.9.8
  - firstrunwizard: 1.1
  - gallery: 16.0.2
  - market: 0.2.3
  - notifications: 0.3.2
  - polls: 0.8.0
  - provisioning_api: 0.5.0
  - security: 0.0.2
  - systemtags: 0.3.0
  - templateeditor: 0.2
  - updatenotification: 0.2.1
Disabled:
  - external
  - federation
  - theme-example
  - user_external
Are you using external storage, if yes which one: NO
Are you using encryption: yes
Are you using an external user-backend, if yes which one: Can’t see
Client configuration
Browser: Chrome Version 63.0.3239.108
Operating system: Fedora 27
Logs
Web server error log
[Wed Jan 24 18:55:16.931955 2018] [:error] [pid 20626] [client 127.0.0.1:35464] PHP Fatal error:  Method OC_L10N_String::__toString() must not throw an exception, caught Error: Class 'Symfony\\Component\\Translation\\PluralizationRules' not found in /home/www/owncloud/lib/private/L10N/L10N.php on line 0
ownCloud log (data/owncloud.log)
{"reqId":"UesWlGjqEO5YBAqds6nv","level":3,"time":"2018-01-24T18:10:24+00:00","remoteAddr":"127.0.0.1","user":"Tutul","app":"PHP","method":"GET","url":"\/owncloud\/index.php\/settings\/admin?sectionid=general","message":"Method OC_L10N_String::__toString() must not throw an exception, caught Error: Class 'Symfony\\Component\\Translation\\PluralizationRules' not found at \/home\/www\/owncloud\/lib\/private\/L10N\/L10N.php#0"}
Browser log
Request URL:https://******************/owncloud/index.php/settings/admin?sectionid=general
Request Method:GET
Status Code:500 Internal Server Error
Remote Address:******************:443
Referrer Policy:no-referrer