As a response to a call to investigate the fundamental aspects regarding educational theory, research, designing and teaching of language massive open online courses (MOOCs), this study first developed a Community of Inquiry (CoI) observation protocol, to observe the existing teaching, social, and cognitive presences in language MOOCs, and tested its reliability using g-theory analysis. The results showed that the developed observation protocol is reliable, as evidenced by the large proportion of variance attributed to variation across courses rather than across raters. A follow-up d-study suggested that five and 11 raters were enough to reach moderate and substantial reliability coefficients, respectively. The study also identified exemplary practices that reflected high-level CoI presences in language MOOCs. The result not only highlighted the need to conduct observational studies to disentangle the dynamic interchanges that occur in language MOOCs, but also provided practical guidelines to language educators interested in designing and teaching their own MOOCs.