from torchmetrics import MetricCollection
from torchmetrics.text import BLEUScore

scores = MetricCollection({
    "bleu-1": BLEUScore(1),
    "bleu-2": BLEUScore(2),
    "bleu-3": BLEUScore(3),
    "bleu-4": BLEUScore(4),
})

preds = ['the cat is on the mat']
target = [['there is a cat on the mat', 'a cat is on the mat']]

scores.update(preds, target)

print(scores.compute())