Heritage language research: a methodological synthesis of the past 25 years

The present review synthesises methodological trends in heritage language research from 2000 to 2025 by analysing 428 empirical studies published in English in peer-reviewed journals in accordance with PRISMA guidelines. Results reveal a regional bias towards North America and an English-centric emphasis in language pairings, which limits global representativeness. The literature predominantly addresses morphosyntactic phenomena using offline lab-based tasks—notably elicited production and comprehension accuracy measures—while online psycholinguistic methods remain under-utilised. Furthermore, most studies target adult populations, constraining insight into developmental trajectories across ages. Transparency in data, materials, and analysis code is increasing, although it is not yet fully consistent with current Open Science/Research standards. In view of growing interest in heritage languages and an expanding evidence base, we propose several methodological priorities to strengthen the field: broaden linguistic diversity, compare WEIRD and non-WEIRD contexts, and incorporate real-time experimental measures together with advanced data-analysis methods to investigate heritage language phenomena.