You got liberals and leftist mixed up

In the context of Germany, "liberal" means being for capitalism unbridled by the state but still generally progressive policies culturally, with more rights for minorities and such. The corresponding party is FDP. So in some ways it's the exact opposite of the US idea of "liberal".

Someone considered "left" would be for more social policies and government control of capitalism (traditionally SPD), extreme left would be following tenants of communism, opposed to the US and friendly with Russia (The party The Left and the new Sarah Wagenknecht party)

Someone considered conservative or "right" would be against social policies and try to reduce control of capitalism (CDU) extreme right would be plain fascists (AfD), ironically also aligned with Russia now.

The Greens are a special case, since they were originally a single issue party concerned with environmentalism, but since the SPD has largely vacated their social policies since Schröder was chancellor, they have become more and more the new "social" party.

There are also a huge number of smaller parties that are unable to reach more than five percent, which is necessary to be included in the govenmental body of the Bundestag. Most of those are single issue parties (there is even a beer party). The FDP has become so unpopular that it might also share that fate soon.

To come back to your original point, there were no "liberals" when Hitler was elected. There were conservatives, socialists and communists. The conservatives aligned themselves with the fascists and the socialists and communists were outlawed and thrown into jail/executed.

I don't at all understand how you got your definition of "liberal". I think anyone who could conceivably be called a "tankie" would bristle at being called liberal.

Liberalism is a political and moral philosophy based on the rights of the individual, liberty, consent of the governed, political equality, right to private property and equality before the law.[1][2] Liberals espouse various and often mutually warring views depending on their understanding of these principles but generally support private property, market economies, individual rights (including civil rights and human rights), liberal democracy, secularism, rule of law, economic and political freedom, freedom of speech, freedom of the press, freedom of assembly, and freedom of religion.[3] Liberalism is frequently cited as the dominant ideology of modern history.

https://en.m.wikipedia.org/wiki/Liberalism

Both of our American parties are liberals. However, most Americans use the word to mean "progressive".

I think "Leftist" starts at anti-capitalism and goes from there. I half jokingly say a progressive is someone who thinks the system is broken and must be fixed. A Leftist is someone who thinks the system is working exactly as intended and must be destroyed.

To throw one more into the mix:

“Left” and “Right” came from the UK parliamentary system where the representatives of the two major parties sat on the left and right side of the speaker of the house in the House of Commons.

It just so happened that the ones on the right had conservative values (keep things as they are, don’t spend what we don’t have, local economy first, preserve traditional values) while those seated on the left had liberal values (let’s make things even better, spend for the future, improve the global economy, make life better for all our constituents).

That was the starting point for what it’s all morphed into today.