Many terms are in journals, but they're also spoken to people in the same group. I honestly can't even think of a good example of a case where people would not be familiar with technical words and not understand them, if they've already been trained. Regarding medical terms, that's completely untrue. All the initial learning is done in medical school, and a lot of it is through verbal teaching, only reinforced by textbooks. Yes, there's a lot from journals, but that only adds more information to the fundamental things we know.
There are plenty of new terms entering the literature at any time, and if you've been in such circumstances you'd quickly realise that the way that terms are said can vary vastly from lab to lab, particularly if a research team is lead by a particularly strong personality and has a core group that have been there for a while.
If your doctors only did their learning in medical school I'd strongly recommend finding new yourself a new set of doctors. Different medical schools speak different ways with the same terms as well. Not even spelling is consistent across the medical community. For example, Americans can't spell Haemophilia.
I feel like this whole "language is fluid" is really taken out of context. Yes, language is fluid and evolves. There are changes happening every day with new words being added to the lexicon. Old words can take new meanings (for example, "they" now being more often used as a singular pronoun to refer to neutral genders). But that's where the evolution is -- new words and definitions, and the other is in regional variation with minor phonemic changes that apply to whole groups of words -- not one single mispronunciation. There are a few instances where mispronunciations become so common that they're even added to the dictionary, but that's extremely rare as a whole.
The 'singular they' is actually very old in the English language. Not using they as a singular pronoun was the more modern change, but that's weakened again. I for one prefer the 'singular they' to many of the alternatives, particularly as people no longer accept 'he' as a gender neutral (or gender non-specific) pronoun.
Singular pronunciations change all the time, while the sum of their parts is seen in large scale shifts in languages. Don't confuse the study of averages with the individual parts. It's very possible (and common) for singular words to change for one reason or another, particularly when dealing with what were loanwords. For example, there are two perfectly acceptable readings of the term 'Celtic' in modern English, though one of them was a 19th century invention.
There are plenty of mispronunciations that are added to the dictionary, how do you think we got American English?
As for proper names like what I brought up initially with Qin... that's not subject to "fluid" changes in languages. You were given a name, and there's only one way to pronounce it -- by the way you (and by extension, your parents) pronounce it. For example, Stephen is often pronounced "Steeven." But if you (as an English speaker) pronounce it like that for Stephen Curry, you're wrong, period. Then as for names that are difficult to pronounce, like Qin, as long as you come close, that's acceptable. Pronouncing Qin and Tokimune as Kin and Tokeemoon are bad because at least as an English speaker, you're easily capable of doing better. Even if Sean Bean pronounced Tokimune as "Tokeemoonee" instead of "Tokeemooneh" then that's fine.
Proper nouns shouldn't be fluid, at least when speaking with the person they are referring too. However, with terms of historical leaders and figures they most certainly are. The harrowing tale of how the English language settled on the name "Jesus" is but one example of how much names can be changed over the generations.
If you read up earlier, you can see my own discussion of dealing with proper names when talking with and about a living person. Thing become different when talking about people who have taken on larger than life characteristics though. Dr. Seuss could tell you a thing or two about that.
I do agree that there is a fairly standard pronunciation of Qin Shi Huang and Hojo Tokimune that we should try and have within the context of the game, but at the same time both are fairly far from their original pronunciations. Qin Shi Huang oddly enough is nearly nothing like the Emperor himself would have said it, it is instead the Mandarin Chinese for his title.
I won't argue with that. Although one good teacher that teaches the correct way can go a long way.
Teachers can only teach as they were taught, or as they taught themselves. Variations that they have heard will be spread. There's literally nothing wrong with that (for the record the use of literally' to mean 'figuratively' or add emphasis is also very old within the English language).
Basically what I just said
There were some differences there.
I'm a linguistics nerd, so I can't help it.
Judging by how you're speaking you're a prescriptivist. A prescriptivist linguistics nerd is an oxymoron. Linguistics celebrates the differences and variances in language, you seem to emphasise the opposite.
Yes, there are different ways, as long as they're in the realm of acceptable. For example, Aeschylus. It can vary (
https://en.wikipedia.org/wiki/Aeschylus), but if you pronounce it as "Eshilis," then that's wrong. Pronouncing Achilles as "A chills" is wrong. Things like that. They are traps as much as Qin is for Kin, but we're taught to know better.
Now, on the point of being a "linguistics nerd", for the love of all that is spoken, do not try and render your pronunciation to English orthography like that. It literally helps nothing.
It's like saying: "It's 'mome raths', with 'rath' to rhyme with bath". It is entirely unhelpful. Even assuming that the consonants are kept the same between readers, it's the vowels that cause problems as they vary so much between readers. For example, bath can be read as /bɑːθ/ or /bæθ/ in the example before, meaning that description in text is unhelpful. Aeschylus is generally pronounced with an unvoiced final vowel, and so I could render it into English orthography as: Ehskilus, Eskulus, Eskilus, Eskulas, Eskilis, etc. I'm sure a lot of readers would read each of those differently as well, and I doubt many would read it with my original intent. Even going for "Eh-sk-lus" doesn't help, as many speakers will take different sounds from each of those.
I'm all for promoting an understanding of how we traditionally pronounce such things in English, and for specialised terms that aren't rapidly changing (as you seen in science and medicine), mostly names like Qin Shi Huang, I do agree it's a good idea to teach the standard form to people. That doesn't apply to absolutely everything however, and it's perfectly acceptable for people to have other forms, the forms we use themselves are already vastly different to the originals.
To be fair, I didn't get past the Knight's Tale before I needed a break, and I haven't returned to it yet. But with a little knowledge of the philological history of English, it's definitely doable. 
