Hello @Juan , yes, that's correct! The $2.5 per audio/hour price for the Speech Translation service includes 1 audio input and output, up to 2 text translation languages using standard or custom Speech to Text and standard Translation. This means that this charge applies up to 2 text translation languages only.
If you want to translate into 3 or more languages, you will need to reference the Azure AI Translator Text Translation pricing page, and you will be charged extra according to that pricing.
Though you will not use Azure AI Translation, but the pricing is compared with respect to that service.
I hope this helps clarify things for you! Let me know if you have any further questions or concerns.