Another problem I'm having (hopefully the only remaining) is with
topics. I can create a bunch of topics, but when I try to attach topics
to an article it just says "No topics".
Unless I change the parameter f_language_selected=18 to
f_language_selected=1
Then I get a list of all topics but I can't attach them as it thinks
that the article doesn't exist in that language.
I should add that the articles in question are in Swedish, so I created
that language myself.
Yes, that is a bug in 2.4. In version 2.5, coming out March 1st, you
will be able to translate topics and so the list wont be empty anymore.
The change you made is perfectly fine and wont cause any problems.