I took an interest into his biography, he grew up in Ghent and was only fluent in French, Flemish and Latin. He only learned some Spanish to be accepted by the local nobility after taking the Spanish throne.

If he was talking about German he probably meant Dutch, since they where considered the same "language" at that time. ( Interestingly German used to be called "High Dutch" in English - with "Low Dutch" denoting modern day Dutch, Flemish and Low German)

It's reported that his "High Dutch" was very limited, probably enough for a horse.

Since Germany has no political centre like Paris or London it's pretty hard to tell how his German would have sound like, the modern pronunciation standard was mostly unknown before the age of radio. (For comparison Yiddish is 80% medieval German)

No evidence he spoke Italian, though his possessions covered Sicily and Sardinia, but I'd be very surprised if they spoke anything like the dialect of Firenze which became modern Italian.

And I've met more than one Canadian claiming that Quebecois is just old French. ( likewise Geordie is old English)

Tl;Dr ... his languages didn't really sound like they do today.