In Forth, comments are written like this:

2 2 ( Now add these numbers...) +

The English in parentheses is a comment. The space after `(' is important! ( is a Forth word (marked IMMEDIATE) that discards the rest of the line, till the first `)'. Without the space, Forth would look for a word `(Now' instead.

Like everything else in this language, comments can be implemented by the user. Try that in your favourite high level language!