From now on, invoices will be generated in a language you've selected in your Biz Settings.
Now you can delete unwanted chats with any contact. By default, it'll delete automatically synced chat messages. If you've saved any message/media explicitly, those won't be deleted. To do so, turn on "Delete Saved Messages".
To delete the chat, go to:
CRM > Chats > Select Contact > Click on Delete icon in top-right corner.