Hey, I'm from Germany and planning to travel from Vietnam over land to China

Annika, it's possible to get a 2 months tourist L type for you. As you can't provide round-trip flight tickets, I think it's better to apply for a visiting friends type entry permit. Actually it's the same as a normal L type, but you can indicate on the application form that you will visit your friends. An invitation letter and passport/ID card copy from your friend are required for submission.

The Travel agencies here told I can only apply for 1 months tourist L type or 2 months 2 entries but I've to leave China after 4 weeks and then enter again! Do you know if there's another way to get directly 2 months and one entry?

Annika, usually, it’s not easy to get a tourist L type with stay duration of 2 months. You can just apply for a single-entry tourist L type with stay duration of 30 days, and then you can apply for an extension before it expires to get another 30 days without leaving PRC.