Bitnami packages and configures already existing applications. We can only offer support and help on basic and most frequent application configurations. Always based on the default configuration or on our guides. The documentation of Mautic about how to change the language of the application can be found here
Probably someone with more experience and knowledge about that application can help you better than we can. We suggest you to post your question on the official support forums of the application so others can help you with your issue.
Do not hesitate to ask us any other question about any of our solutions.