In an interview with Swiss business journal Finanz und Wirtschaft published this week, Dougan, who is stepping down next month, counts not learning the language as one of his regrets.
“I speak some French and Japanese and consider myself talented at languages, but I was just too busy,” the American expat is quoted as saying.
German is one of Switzerland's three official languages, along with French and Italian.
It is spoken by residents of Zurich and a majority (around 64 percent) of the Swiss population.
Dougan, 55, is being replaced by Tidjane Thiam, who has served as CEO of UK-based insurer Prudential since 2009 in what some media have described as an ouster as Credit Suisse continues to reel from massive US penalties and faces increasing regulatory scrutiny.
In March when the change was announced, Dougan said in a statement issued by the bank that it was “the right time for the organization and for me to transition out of the CEO role.”
Thiam, 52, a French-Ivory Coast national, managed to triple the value of Prudential's share price during his tenure and he speaks German, in addition to fluent English and French.
Credit Suisse's share price fell from 90 francs to less than 25 francs during Dougan's time as CEO.
But Dougan, who received an MBA in finance from the University of Chicago's Booth School of Business, defended his record, noting that the bank had always paid dividends, which should be included in the return for investors.
He also defended his role in helping Credit Suisse steer through the financial crisis without having to rely on government aid (unlike UBS, which required a bailout from Bern to avoid bankruptcy).
“My answer was and is always the same: it was right what we did,” Dougan said.
He said it was important to run a business “conservatively” so it is not dependent on anyone, “certainly not the taxpayer”.
Credit Suisse is now a “uniquely balanced big bank - with a strong brand, both in asset management and in investment banking”.
Dougan said it was too early to talk about his future although “I suspect I will do something completely different”.
He said he had not decided whether to return to the United States.
Presumably, he will soon have time to take German lessons.