Back in the day, there was a horribly believable urban myth that Word for Windows was actually written in Prolog...
Windows (circa NT) certainly used to contain a lump of Prolog, which handled network configuration. The rules were buried in a DLL, if one knew where to look.
Going back to OP's question. PL/I is a derivative of ALGOL-60, as are the Pascal family (Pascal, Ada, Modula-2 etc.) and the BCPL family (BCPL, C, C++, Perl, Python etc.). Non-derivative languages include APL, Forth, Lisp, Smalltalk, Prolog and arguably Rust.
I still use a modern Pascal implementation on occasion, but consider myself "adequately read" as far as language history and philosophy are concerned. That leaves me with very little patience for the mutual hostility of the Pascal and C communities.
Judging by what I see in the Free Pascal (compiler/libraries) and Lazarus (IDE) forums, newcomers to the Pascal family of languages have a bit of trouble with the language structure (syntax) and runtime behaviour (semantics) but more than anything else they object to the lack of braces as block enclosures. They object somewhat less to Pascal's relative verbosity than they used to, since modern C has largely adopted Pascal's strict type checking etc.
On unix-based systems there is this as a fortune cookie:
Speaking as someone who has delved into the intricacies of PL/I, I am
sure that only Real Men could have written such a machine-hogging,
cycle-grabbing, all-encompassing monster. Allocate an array and free
the middle third? Sure! Why not? Multiply a character string times a
bit string and assign the result to a float decimal? Go ahead! Free a
controlled variable procedure parameter and reallocate it before
passing it back? Overlay three different types of variable on the same
memory location? Anything you say! Write a recursive macro? Well,
no, but Real Men use rescan. How could a language so obviously
designed and written by Real Men not be intended for Real Man use?
I think that a C user will find PL/I somewhat alien, but would suggest that the learning experience will be very much worthwhile.
MarkMLl