source_lang = "en"
target_lang = "fr"
prefix = "translate English to French: "
def preprocess_function(examples):
     inputs = [prefix + example[source_lang] for example in examples["translation"]]
     targets = [example[target_lang] for example in examples["translation"]]
     model_inputs = tokenizer(inputs, text_target=targets, max_length=128, truncation=True)
     return model_inputs