If you notice that Mana is writing in American English, you can change this to Australian / British English by completing the following steps:
When creating a document with Mana, if you notice the text appearing in American English, in the "What should I change?" box (replacing Magic Actions)
Get Mana to update the language used by typing and submitting "Use Australian/British English"
Your writing will be updated and Mana will remember for future documents to use Australian/British English.