  We introduce a semiclassical theory for strong localization that may arise in
the context of many-body thermalization. As a minimal model for thermalization
we consider a few-site Bose-Hubbard model consisting of two weakly interacting
subsystems that can exchange particles. The occupation of a subsystem ($x$)
satisfies in the classical treatment a Fokker-Planck equation with a diffusion
coefficient $D(x)$. We demonstrate that it is possible to deduce from the
classical description a quantum breaktime $t^*$, and hence the manifestations
of a strong localization effect. For this purpose it is essential to take the
geometry of the energy shell into account, and to make a distinction between
different notions of phasespace exploration.
