T5Model predict <UNK>

config = T5Config(num_layers=12,
num_decoder_layers=12,
pad_token_id=0,
es_token_id=VOCAB_SIZE + 2,
model_parallel=True,
vocab_size=VOCAB_SIZE,
num_heads=12,
d_model=1024,
d_kv=64,
d_ff=3072,
decoder_start_token_id= VOCAB_SIZE + 1,
)
model = T5ForConditionalGeneration(config)
this is my T5 model config.
epoch is 200 .I use it to train a translation model,
but the results of prediction is UNK.

How can I use T5ForConditionalGeneration to train my custom model?
my config is right?