"Do you focus on rich, internet savy countries like Holland or Belgium? Or, do you focus on the next two largest languages online: Mandarin and Spanish? " - Good question

In biz speak (or probably in non-linear programming too), i guess it would be where the different curves meet, the converging point of per capita potential revenues, the volumes (current and future), resources required to tap the market.

Practically this is how the decision tree may look like:

if one has less resources, then it may be wise to tap the market that has the highest per capita of potential revenues(while having reasonably enough volumes)

If one has medium level of resources, then still tap the high per capita market first with the least amount of resouces spent, then once the biz model is validated, deploy the resources for the future biggie market (high vol, low curret potential per capita revenues)

If one has billions to throw like Google, then of course, throw the money in tapping the future biggie and buy off any of the small amart start ups in the developed markets.