Access to timely health guidance remains critically limited in rural Nigeria due to physician shortages (23.3 per 100,000, far below the WHO-recommended 100), poor connectivity, language barriers, and high burden of endemic diseases including malaria (over 100,000 deaths annually) and Lassa fever (172 deaths in 2025). This paper presents HealthHub, an offline-capable, multilingual, rule-based expert system for symptom triage aligned with Nigeria Centre for Disease Control and Prevention (NCDC) and World Health Organization (WHO) protocols. The system implements 26 clinically derived IF-THEN rules covering emergency, high, medium, and low urgency conditions, with a novel safety gate mechanism (EMERGENCY_MIN_SYMPTOMS = 2) designed to reduce false-positive emergency escalation from non-specific single-symptom presentations — a critical vulnerability identified during prototype testing. Multilingual support for English, Nigerian Pidgin, Hausa, Yoruba, and Igbo was achieved through static react-i18next localization, with symptom labels mapped to standardized fact keys for language-agnostic rule evaluation. Evaluation across 63 structured test cases confirmed 100% emergency classification consistency, average rule evaluation time of 0.003 ms in the JavaScript engine (end-to-end approximately 767 ms on mid-range Android devices), full offline operation, and Nigeria Data Protection Regulation (NDPR) compliance. A preliminary usability study with 16 participants across Nigeria and Cameroon yielded a mean overall satisfaction score of 4.19/5 (81.3% positive rate). The system is publicly accessible as a Progressive Web App. HealthHub demonstrates the feasibility of equitable, explainable, offline digital health tools in low-resource Nigerian settings, contributing toward Universal Health Coverage goals.

Symptom triage; rule-based expert system; multilingual support; offline healthcare; Nigeria; equitable access; NCDC; WHO; React Native; Progressive Web App