Agent language settings will determine whether a translation is fired and the language pair of the translation request. While the customer language will vary between conversations, the default language will determine the language that the agent is assumed to understand and write in (typically English).
Spoken languages, on the other hand, are the ones the agent is presumed to understand and forego the need for translations. If the conversation language matches any of these, Unbabel won't start and no translations will take place. If the agent tries to use Unbabel the translation will not be requested.
Look for the Agents section of the page to find the list of agents. You can use the search email field to find specific agents, typing their email addresses. Matching results will appear, even if the agents were listed in a different page. This will display all agents that are or have been authorized, along with their spoken and writing languages. If you click the agents' email you can make any changes to the language setup.
Edit the language settings as needed and save your changes.