Learning a foreign language is definetly going to improve your career prospect and its a good decision. So, as for Spanish or German, my suggestion will be German or French though there are more Spanish speaking countries.But many banks, world organisations, tech companies and of course fashion companies use French and German. Just to name a few well known, most successful companies in the world that are based in French or German speaking countries. Few of the many famous brands are Loreal, Dior, Capegemini, Mercedes, BMW. So, as per me it will be German .

Hope this helps..take care.