I have the following returned. However, longer strings yield FR results, not 100% sure why. I assume it is a lack of training sentence pairs. Good luck!

سلام

Returned from this snippet.
from transformers import MBartForConditionalGeneration, MBart50TokenizerFast

article_fr = "Bonjour"

model = MBartForConditionalGeneration.from_pretrained("facebook/mbart-large-50-one-to-many-mmt")
tokenizer = MBart50TokenizerFast.from_pretrained("facebook/mbart-large-50-one-to-many-mmt", src_lang="fr_XX")

model_inputs = tokenizer(article_fr, return_tensors="pt")

generated_tokens = model.generate(
    **model_inputs,
    forced_bos_token_id=tokenizer.lang_code_to_id["fa_IR"]
)
print(tokenizer.batch_decode(generated_tokens, skip_special_tokens=True))