I believe you're correct; I'm not aware of any other language with a left-associative ternary.

This will be deprecated as of PHP 7.4[0], and will cause a compile error in PHP 8.0.

However, instead of switching straight to right-associativity, PHP will require explicit parentheses to disambiguate nested ternaries.

[0] https://wiki.php.net/rfc/ternary_associativity