  What can pre-trained multilingual sequence-to-sequence models like mBART
contribute to translating low-resource languages? We conduct a thorough
empirical experiment in 10 languages to ascertain this, considering five
factors: (1) the amount of fine-tuning data, (2) the noise in the fine-tuning
data, (3) the amount of pre-training data in the model, (4) the impact of
domain mismatch, and (5) language typology. In addition to yielding several
heuristics, the experiments form a framework for evaluating the data
sensitivities of machine translation systems. While mBART is robust to domain
differences, its translations for unseen and typologically distant languages
remain below 3.0 BLEU. In answer to our title's question, mBART is not a
low-resource panacea; we therefore encourage shifting the emphasis from new
models to new data.
