The tracheal deviation seen in this chest x-ray is due to left lower lobe collapse. This has a classical appearance of a 'double left heart border,' or a 'sail sign' (orange). The second heart border (curved arrow) is due to the dense edge of the collapsed left lower lobe, which has been squashed into a triangle or sail shape.
Note that the left hemidiaphragm cannot be followed all the way to the spine. This is because the left lower lobe sits directly on top of the diaphragm, and as it no longer contains air, it is of the same soft tissue density as the diaphragm and therefore blends into it.