How is Langmuir adsorption isotherm different from Freundlich's?
There is a fundamental difference between both models.

Langmuir's model was a theoretical construct, while the Freundlich isotherm is empirical.

In the Langmuir model, it is assumed that at maximum coverage, there is only a monomolecular layer on the surface. This means that there is no stacking of adsorbed molecules. The Freundlich isotherm does not have this restriction.