lean
The German word 'schlank' is used to describe something or someone that is thin and fit, often in a healthy way. It can refer to a person who is not overweight and has a toned physique, or to an object that is slim and not bulky. The word is often used in a positive context to describe something that is well-proportioned and aesthetically pleasing.
She is very slim.
This is a straightforward usage of 'schlank' to describe someone's physical appearance. It denotes the fact that the person in question has a slim figure.
I have to become slim.
Here, 'schlank' is used in the context of personal health or fitness goals. The speaker is expressing a desire to become slim, likely through dieting or exercise.
He thinks she is too thin.
Here, 'schlank' is used to express an opinion about someone else's weight. The implication may be that the person in question is unhealthily thin, though this would depend on the context.