When are you allowed to remain on the left-hand lane in this situation?

In the context of German traffic laws, remaining in the left-hand lane is generally reserved for overtaking slower vehicles. The specific case you are referring to involves parameters related to vehicle width.

If you're allowed to remain in the left-hand lane when your vehicle, including its load, is a maximum width of 2 meters, it means that vehicles fitting these criteria can use the left lane for longer stretches. However, simply being 2 meters wide according to the registration certificate does not automatically grant the right to stay in the left lane; actual measurements including the load are the determining factor.

Essentially, if both aspects are met—your vehicle width with load being 2 meters or less and having a properly registered width—only then can you legally remain in the left lane. It's crucial to consider both sets of criteria together based on German road regulations to ensure compliance and safety.