I think a good starting point is what countries/regions interest him, enough to pursue opportunities once outside of universities. Big orgs will have language suite software so accessibility is there, if expected from a role perspective
Any language acquisition is going to diminish under the use it or lose it. More useful potentially, is understanding the cultural nuances in parallel. So a simple enhancement of his Spanish could be, au pair for a couple of months, or summer school/camp aide etc.
Mine au paired in Madrid for 3 months in between Y1 and Y2, and spent 6 months in Spain in Y3 where all subjects at her Spanish university were taught in local language, no concessions made for International students.
Re potential Arabic if developed further, using MSA will help enormously on the written, formal side of work but he really needs to hone in on what parts of the ME region may be of interest to him in professional life. Egyptian, Levantine, Gulf or Moroccan Arabic will all work as spoken, he can develop the regional differences if needed.
Anecdotally, my DD didn't expect to use her Egyptian Arabic at all post studies, yet months into her work (graduated last Summer), with developers based in Cairo, she culturally, was an immediate fit for a project (did 6 months study in Egypt).The next one has her on a cross-border project with EU, selected due to her fluent Spanish. Another friend's DD who did Russian and Ukrainian (spent one year in Kazakhstan) has resulted in the 'tap'. She operates now on a desk where I know no more, her YA and living with a local family accelerated her acquisition of the regions making her viable approach across many industry sectors.
Sorry long, but in summary, so many of these posts become about the language acquisition alone, but I think he needs to consider what he can leverage from which ever option he has on offer from his university, be really proactive in both cultural and language acquisition opportunities, but ultimately, choose what he actually likes to learn, rather than what he thinks would be more useful (at this stage), given that it is only one semester.
Good luck to him!