~ Would it be difficult to get licensed after leaving graduate school?
All things are possible. In general, it's a lot easier to get a teaching certificate if you go through a state accredited teacher certification program. Some states have alternative certification programs but these programs are primarily geared towards placing new teachers in some of the most challenging schools where there are acute shortages. This typically results in being placed at an inner city school in difficult neighborhoods.
Teaching is already stressful enough. If you went through an alternative certification route, you might have to take evening courses, weekend courses, and/or summer courses which would be exhausting when added to the responsibilties of being a classroom teacher.
~ Do universities offer teaching licenses as part of their academic programs in other fields?
If you mean could you pursue a journalism degree and get a teaching certificate as a journalism teacher, this would depend upon whether you took secondary education classes in the school of education. People who graduate with non-education degrees do not get teaching certificates.
~ Do different states/jurisdictions require different teacher training in order to be hired in a public school?
Each state mandates certification requirements for teaching.
The University of Kentucky maintains a website about current requirements for state certifcation in each of our states.
~ What if I change my mind about professional teaching once I've progressed in my other career?
I don't understand the question.
If you don't teach, you don't teach. In time your certificate will expire. If you wanted to resume teaching, you'd have to be recertified. This would typically mean having to take extra courses and possibly having to take one or more standardized tests to renew your certificate.
Should it go alongside my studies in journalism or linguistics (or whatever it ends up being)? Or should it wait until I've established myself in that other field, and have decided (under the particular circumstances, which I couldn't ascertain now no matter how fastidious a planner I were) that I really do want to teach?
Again, it's a lot easier for you to get your certificate along with the training you'll need to start as a novice teacher if you go through a regular ed program while in college. Depending upon the college in question, this could add an extra year (or more) to a standard four year program.
One option for you to consider is the possibility of employment in a private schools. Depending upon which state you're in, private schools don't necessarily require certification. Certification will help - but if you have real life experience in journalism or whatever field you choose to pursue, that experience could be quite useful. If you decided to consider the possibility of pursuing this route, you could take some general education courses as electives. By doing this, you'd have some of the background you need as a teacher even though you wouldn't be certfied.
I only know one teacher who went this route. She was a free lance reporter/photographer and she got a teaching job at ACS Beirut (American Communtiy School) in Beirut, Lebanon. She had no background in education prior to working at ACS Beirut but she knew the ins and outs of international journalism which made her a good asset for the school.
If you're intereseted in the possibility of private education, here's the website of a recruiter for teachers in the private schools. Visit their website and see what they have to say.
Please be aware that in general, private education salaries and benefits are lower than those of the public schools. Intrinsic job satisfaction in these schools will generally be higher but lower salaries tend to result in higher turnover.
According to ISM, the annual rate of turnover in public schools is 12.4%. The annual rate of turnover in large private schools is 18.9%. The average turnover rate in small private schools is nearly twice that of public schools: 22.8%.