As far as I know, "internal stability" involves inflation, unemployment and economic growth. So the effects of an appreciation (an appreciation, according to the AD formula has a contractionary effect on the economy) on these:
Inflation - a reduction in imported (pay less = lower price) and cost push(cheaper to purchase inputs o/s) inflation
Economic growth - a reduction in economic growth (AD) through decreased competitiveness for exporters = less X as well as more imports flowing out of the economy as it's cheaper to purchase overseas and thus M will increase.
Unemployment - as a result of firms becoming less competitive, as labour is a derived demand, workers will lay off workers and thus increase unemployment