In some ways, it’s much better to learn fewer languages rather than more. I would certainly recommend starting with fewer. But once you’ve built up to it, there can be reasons for working on many languages at once rather than just a few or just one.
That’s the path I’ve chosen. I’m currently working on nine different languages; two of them I practice daily, three every other day, and four of them about once a week. I only do a few minutes for each study session for an individual language, partly so I don’t tire my brain out (it’s deeply important to try to avoid overworking the brain if we want to be able to keep up a consistent and long-term life of intellectual activity), and partly because as a stay at home dad I only have a few minutes at a time to do these sorts of things.
There are lots of good reasons not to do a bunch of languages at the same time. The biggest is that it drastically slows down how quickly each language can be learned. That obviously happens in part because if you’re learning four languages at once, you have a quarter of the time to devote to each (on average) as you would if you were only learning one.
But I think it’s even more than that. I think that learning four languages rather than one wouldn’t make you go a quarter the speed in each language, but probably even considerably more slowly than that. To keep four going rather than one requires a more rigid discipline and schedule that will clamp down on some of the room for feeling inspired that you might be able to get in a simpler system. And in learning four new languages the brain is being called on to do something that’s not four times more complicated than learning one but in a way, ten times more complicated.
Still, clearly for me the arguments against, though I’ve weighed them very seriously, haven’t dissuaded me. Most importantly, I’ve decided at this point that I don’t need to be in a great hurry to learn any one of my languages, so going slowly is okay by me. I’m in this for the long haul. I will get benefit from this, if slowly, so long as I stay consistent, which I plan to do (barring any really big changes in my life).
Given that opportunity for patience, I opt for the smaller advantages of studying several at once, since those advantages better match my goals. The languages I practice once a week are getting better only very slowly, not fast enough to matter much—but at least they are not getting worse. For me, being able to maintain the languages I’ve studied is the biggest benefit of doing several languages at once.
I’m able to improve at a decent pace in the languages I care most about (German and classical Greek, at this point), and to make at least perceptible improvement in the languages I practice every other day (Latin, French, Italian). And as I make slow progress in these, I am able to make use of the languages in the sorts of ways I want to be able to use them at this point, puzzling out phrases that show up in quotations in the books I read, or making sense of the original text underlying a translation I’m reading when I have a question.
With time, I hope, I will become pretty adept in all nine (and many more besides, I dare to wish). In the meantime, they are all kept at the level I want to have them at, and with each passing month, I find I’ve grown a little bit more competent in each, without even having noticed it happening.