"Monday is the first workday of the week."
Translation:Montag ist der erste Werktag der Woche.
Depending on where you are in Germany or Austria, "Werktag" or "Arbeitstag" will be the most common, if not the ONLY word used for 'workday' in your region. In my experience, Arbeitstag is prevalent
In German we say "Arbeitstag". This is also the case in the employment contracts of employees.
My understanding is that "Werktag" and "Arbeitstag" are different concepts. "Werktag" seems to be a legal definition referring to legal working days. Monday through Saturday are Werktäge. Sunday is not. While Arbeitstag refers to an individual's work schedule. Sunday is not a Werktag, but for a Priest it is an Arbeitstag. Also, although Monday is a Werktag, if a restaurant is closed on Mondays then Monday is not an Arbeitstag for the cook.
This exercise though calls for a translation and the context is not clear. Yes Monday is the first Werktag. But for most workers Monday is probably also the first day they work, and therefore also their first Arbeitstag.
I recommend that Arbeitstag also be accepted as a correct answer.
The correct translation of "workday" is Arbeitstag. From Webster's dictionary: "Definition of workday 1 : a day on which work is performed as distinguished from a day off 2 : the period of time in a day during which work is performed On workdays I usually wake up at six o'clock."
The correct translation for Werktag is "business day". From Webster's dictionary: "Definition of business day : a day when most businesses are open : a weekday that is not a holiday Please allow 14 business days for delivery."
As far as I can tell (as a native speaker), her pronunciation is correct.
Because, in German, er is pronounced like ah in most cases. That also happens in British England, for reference.