We analyze the Helmholtz–Korteweg and nematic Helmholtz–Korteweg equations, variants of the classical Helmholtz equation for time-harmonic wave propagation for Korteweg and nematic Korteweg fluids. Korteweg fluids are ones where the stress tensor depends on density gradients; nematic Korteweg fluids further depend on a nematic director describing the orientation of the (anisotropic) molecules. We prove existence and uniqueness of solutions to these equations for suitable (nonresonant) wave numbers and propose convergent discretizations for their numerical solution. The discretization of these equations is nontrivial as they demand high regularity and involve unfamiliar boundary conditions; we address these challenges by using high-order conforming finite elements, and enforcing the boundary conditions with Nitsche’s method. We illustrate our analysis with numerical simulations in two dimensions.