I don't know about PL/I but Prolog kind of cheats, in my opinion, about the reserved words. It is very strict about naming conventions, which is (IMO) worse than having reserved words.
PL/I is syntactically like Algol, or Pascal, or C with more words and fewer brackets. At heart, it's a "normal" block-structured procedural programming language, which proves that a C clone could adopt the same basic idea.