Setting target language codes in mT5

Hi, I’m fine-tuning the google/mt5-base model for many2many translation. The issue is that I do not see any language tag available in the model config (facebook/mbart-large-50 has these included). Normally when generate I would use the forced_bos_token_id (e.g. with mbart-large-50) to force generation of the target language. Are there any pre-defined language codes for mt5, or do I have to add additional special tokens myself ?