AFAIK there is a "service supplement" of about 2 EUR if one buys the Bayern-Ticket from the counter. And the lines at the DB Ticket Counter at MUC are often VERY long. I would rather spend an extra minute on the ticket machine (which "speaks" English)
Now that I didn't know. I have always used the machines, which I believe speak several languages.
The process for buying Ländertickets is a little different. The English language option will probably be something like "Special Tickets".