A content service (engine) was reporting:
28/03/2017 16:12:54  00-Always: Error: Languagetype englishUTF8 has been changed. Previous definition (lang=ENGLISH, enc=UTF8) will be used.
28/03/2017 16:12:54  99-Always: Failed to initialise language settings. Exiting
Although there was no evidence that language settings failed before or after a server reboot, the Content Engine was convinced there was a language issue and would stop immediately.
The only recourse is:
1) Restore from backup
Backup is the best for a large environment, as a reindex could take days. Find backup files from a date prior to error and then overwrite/move to target Content Engine index folder location. Once restored, restart the Content Service and see if it is able to function properly. Check the IDOL Content Service's application.log file to confirm successful startup.
Failing that, a reindex would be necessary. Contant HPE CM Support team for reindex steps for your environment.