I would guess that this is just another nonsensical version of "why do we care if Iran gets a nuclear weapon when 'country X' already has nuclear weapons"... except Germany doesn't (unless you count the U.S. B61s there under NATO agreement)

Why does Germany need another submarine for NATO?

The onboard diesel engine runs when at the surface to charge the PEM cells, which then power the electric motor for propulsion while underwater outside of snorkel range.

In the past, this same practice has been used to charge batteries instead of fuel cells. The only real difference here is that the fuel cells give it a somewhat longer endurance underwater. Diesel-electrics have been championed for their incredible silence and stealthiness for the past 30 years, to the point a 1990's-era Chinese diesel-electric snuck up on US ships during a training exercise a few years ago: http://www.dailymail.co.uk/news/article-492804/The-uninvited-guest-Chinese-sub-pops-middle-U-S-Navy-exercise-leaving-military-chiefs-red-faced.html

Surface or snorkel, fire up the diesels to run an electric generator to hydrolyze ocean water to H2 and O2, and charge the fuel cells.

Frankly, I'd be shocked if the sub were able to haul enough H2 and O2 to power the PEM for months at a time. Those would be absolutely massive fuel tanks.

When it comes to sheer energy density, it's hard to beat fossil fuels.

which is pretty comprehensive, doesn't mention any electrolyzers? It would seem to be a significant feature.

... since these subs have been around for more than a decade.

And it's hardly an indication we should be building more civilian nuclear reactors.

Same goes for hydrogen-powered subs.