The four hyperparameters α e (extended fertility model), β (edge model), γ (distance model), and δ (subtree model), were set by a grid search algorithm, 12 which found the following optimal values: α e = 0.01, β = 1, γ = 1.5, δ = 1 In informal experiments, parameters were tuned also for other treebanks and we found out that they vary across languages.
adjusting the hyperparameters on another language would probably change the scores significantly.