A full-time position pays around 44.000€/year (varying a bit from state to state) which is ~3.650€/month. This goes up over time, up to around 56.500€/year. All of this is public information, TV-L 13 is the keyword to look for (TV-L stands for "Tarifvertrag der Länder", 13 is the group in which PhD students are typically placed by universities). Source in German: http://oeffentlicher-dienst.info/tv-l/west/ Table for salary per month in Euro (relevant row is E 13): http://oeffentlicher-dienst.info/c/t/rechner/tv-l/west?id=tv...
If you don't get a full-time position, you get proportionally less, obviously. In theory if you only have a 50% position and only get 1.800€/month, you should be able to work somewhere else to make up for it. In reality, though, this isn't happening as the professors are tricking the system and are practically abusing the PhD students' dependency on the professor's good-will as he/she is the one who is deciding whether they graduate or not. So even even if a PhD student is only being paid for 20 hours of work a week (50%), they are still expected to work 40h or more.
In non-STEM fields this is sadly happening all the time, sometimes to the extreme where 4 (or even more!) PhD students are being paid from the budget for a single full-time position. In Computer Science, however, I didn't meet a single PhD student that wasn't employed full-time.
Also, that's not so much under what you would do in the private sector. In 'industry', you don't so often start over 1800€/month with a master, even less so in humanities. I mean, it is not rare to start with more, but something like half of people will get less, and the other half won't get much more.
PhD students definitely earn >=2k1 here.
For France and Germany, stipend/wages range roughly from 1200€ to 1800€/mont, so a bit over minimal wage, and definitely under what you could do in the private sector.