Well, if propovijedanje (have I got the right word?) cannot mean "the message" (about the cross, which is the point of the passage), it does miss something imo. But if I'm not mistaken you have not quoted the Croatian NWT for this one.
We have two words: "propovijedanje" (act of preaching, without content) and "propovijed" (message of the preaching, or sermon, for example "propovijed na gori" = "sermon on the mount"),
NWT: " ali Bog je odlucio da ludošcu onoga što se propovijeda spasi one koji vjeruju." "but God decided through the foolishness of what is preached to save those believing." This is literal word-to-word translation.
HBK: "svidjelo se Bogu ludošcu propovijedanja spasiti vjernike." " God saw good through the foolishness of the preaching to save believers." This is literal word-to-word translation too, with "preaching" = act of preaching, no matter what is content of the preaching.
Possible variant: "ludošcu propovijedi" ("foolishness of the message of the preaching", or "foolishness of the sermon") is short, nice, but maybe less accurate than "ludošcu onoga što se propovijeda" ("foolishness of what is preached").
Of course, NWT is NWT, but it is good to see that new editions has some freedom to choose better solutions than English NWT.
But as you say the Croatian NWT does show unusual signs of independence from the English NWT. Maybe we'll see the translator posting here someday...
looking forward... :))