Christa A. answered 06/04/19
Columbia Publishing Course Alum, Writing Coach + English/ESOL Tutor
Hi!
It seems to me that you have a solid foundation of English, at least, though I'm aware that it's easy nowadays to simply plug in what you want to say to a program like Google and let it help you with things like syntax and grammar, so this post may not be entirely reflective of your skills if you used a program like that. Regardless, everyone who's ever learned a second language later in life feels some degree of embarrassment and hesitation and need to apologize about their speech--it's a perfectly normal reaction.
That said, it sounds like you want to be able to a) feel confident enough to not have to rely on technology, and b) to teach an undergraduate course in management science or a related topic.
Given those goals, I would say that online courses may be a good place to start, but you'll probably want to practice in an offline setting, as well. You'll want to find a conversation partner, either online or offline, with whom you feel comfortable--someone you don't feel self-conscious around about your speech. You'll probably also want to tailor the speech to the subject you'll be teaching--there are specific terms in academia that you'll want to feel comfortable not only saying, but also explaining.
Regarding objective measure of your training, I might suggest giving yourself a measurable goal on a program. Something like, say, "I want to be able to answer at least 95% of grammar questions correctly on the WyzAnt subject test." Or, "I want to be able to write 90% of my emails without technological help, and I only want to use technology for vocabulary words in the other 10%." Or, "I want to be able to explain this list of 25 terms to every student." Teaching is trial and error--and not every student is the same, so some students may understand when you explain something one way while others don't, and then you'll need to find another way to explain it to those who didn't understand it the first way. For emails, you might try going old-school with a pen pal who can send you corrections as well as a response.
I will leave you with this last piece of critical advice: ask questions! Tons of them! Never be afraid to ask someone to clarify something, or to explain why they say something one way and not another. You may also ask someone to sit in and listen to your speech patterns, so that they can point out consistent grammar or pronunciation mistakes and help you correct them. But always make sure to understand the reason why something is said or written the way it's said or written, not just simply that it is that way.
Good luck!