Need "intl" lib set to ON

I do not know where to find the setting for "intl" library OFF/ON

Symptom: Site cannot display RSS feeds from comma divided feed URLs.
(using plugins with shortcodes)

Solution: Set "intl" library to ON (maybe?)

Issue: I do not know where to find the setting for "intl" library OFF/ON

Message from a plugin settings page:
intl support Off "intl" library is required for proper sorting of accented (non-ASCII) characters.

- Thank you