[drited]

The evidence is mixed, but some studies (e.g. Jaeggi) did find transfer effects from n back training to fluid intelligence.

It only takes 40 mins a day for 8 weeks to test it out. Much less time than the commitment to learn a new language.

Having tried it, I wouldn't be surprised if the mixed results were due to improper adherence and misunderstanding of how n back works by some study participants. In other words, I think it's possible that results would be less mixed for someone who is already starting from a point of solid intelligence and who is driven enough to put in the hard,focused work to get to higher n back levels.