  A nonlinear wave equation that describes different nonlinear effects in
various fields of research was considered. In two particular cases, this
equation was reduced to the Sine-Gordon equation and the Born-Infeld equation.
Using the slowly varying envelope approximation and the generalized
perturbative reduction method, the nonlinear wave equation was transformed to
coupled nonlinear Schrodinger equations for auxiliary functions. An explicit
analytical solution of a nonlinear wave equation in the form of a two-breather
molecule was obtained. One breather oscillated with the sum, and the other with
the difference of frequencies and wave numbers. The obtained solution coincides
with the solutions of the two-breather molecule found in a number of well-known
equations from different areas of physics. It is shown that in a particular
case of the small amplitude waves, a solution in the form of a two-breather
molecule for the nonlinear Klein-Gordon equation coincides with the vector 0\pi
pulse of the self-induced transparency which is presented under less stringent
conditions compared to the same solution of this equation obtained earlier.
