This paper presents Fleurs-SLU, a multilingual SLU benchmark for speech understanding (SLU) in low-resource languages. Fleurs-SLU contains 692 hours of speech data for subject utterance classification in 102 languages and 944 hours of speech data for multiple-choice question answering through listening comprehension in 92 languages. We extensively evaluate an end-to-end speech classification model, a cascaded system combining speech-to-text transcription and LLM-based classification, and a multimodal speech-LLM on Fleurs-SLU. Experimental results show that while the cascaded system is more robust in multilingual SLU, a well-trained speech encoder demonstrates competitive performance in subject speech classification. The closed-loop speech-LLM matches or surpasses the performance of the cascaded system. Furthermore, we observe a strong correlation among robust multilingual ASR, effective speech-to-text translation, and robust multilingual SLU, demonstrating the mutual benefits of acoustic and semantic speech representations.