Open Moneydance and choose File > Preferences > General.
(On a Mac, choose Moneydance > Preferences > General).
In this window, you can amend the "Locale" field.
Changing the locale field will change the language used in Moneydance.
For example, changing to "French (France)" will amend the language to French.
Changing the locale can also amend certain spelling in Moneydance.
For example, changing from "English (United States)" to "English (United Kingdom)" will change the spelling of Check to Cheque.
Changing the locale may also amend the week start day.
For example, changing from "English (United States)" to "English (United Kingdom)" will change the week start day from Sunday to Monday.