Funny enough, I was referring to natural languages. You're right that in some cases it's very clear that you should learn English, Japanese, etc. but for many others they're actually attracted to a few languages. (e.g.,I like both Italian and Spanish, which one to learn first? Should I learn ancient Greek or Biblical Hebrew first? Would learning modern Hebrew first help me with Biblical Hebrew?) They don't realize that whatever they choose is going to be hard, so it's better just to choose one instead of dabbling.
it makes some sense to spend some time investigating the potential benefits of different languages, maybe learning a bit of each, before moving to italy or whatever, but certainly it's true that choosing a language to devote time will produce valuable results, while evaluating different languages will not
with respect to those particular questions:
many more people speak spanish than italian due to colonial-age history, and portuguese is almost a spanish dialect. for us residents with culinary aspirations, it may be worthwhile to know that spanish is required for most us restaurant kitchens. but italian isn't that far from spanish either; learning either spanish or italian will make it much easier to learn the other
ancient greek or biblical hebrew depends on which books you want to read. the torah is in biblical hebrew; platon, the hellenistic scientists, and the new testament are in classical to koine greek. modern hebrew will help you a lot with biblical hebrew, because it sort of skipped 1800 years of the sort of linguistic mutation that transformed classical latin into spanish and italian, and it is of course mandatory for living in israel. it may be helpful for flirting with israeli backpackers too
