> Many German political parties have extremist elements in them.

No, they don't. Extreme in this context is defined as anti-democratic, those who want to dismantle the system at its foundation and destroy democracy, usually while removing certain groups. That's not something other parties aim for. Sure, they want to change the system, but only to improve the democratic.

> but not okay calling out the far left

There are not many real far left parties in Germany, and usually they are very small, irrelevant and called far left. Most of them are also not against democracy, they are fine with the general system, but argue about details or the economic system. The biggest far left party is "Die Linke", and they are radical left, not extreme left. Maybe they do have some extreme voices, but they are irrelevant.