If you are looking for a South Slavic language version on major streaming platforms, you might find Serbian options:
: You may be able to find it on DVD in the Croatian market, which often includes the Croatian audio track along with English subtitles. The Simpsons (1989) Croatian, English subtitles
However, there are a few alternatives if you are looking for The Simpsons content in Croatian: If you are looking for a South Slavic
: A Serbian dub titled Simpsonovi exists and has been aired on B92. The Simpsons (1989) Croatian, English subtitles