The translation results consist entirely of the special character `<unk>`.

Hello! I’m referring to the tutorials https://opennmt.net/OpenNMT-py/quickstart.htm. Using the downloaded English-German parallel corpus, I have configured the YAML file, created the vocabulary, trained the model, and performed the translation. However, the translation results are entirely composed of special characters such as ‘’. Could someone please assist me with this issue? Thank you for your help.