I'm not sure how to put this without sounding really dismissive of someone, and I'm going to go off at a tangent, but there is a purpose to it, so...
The official English translation is very well directed, they certainly know the script, the intents of the characters, the situations, and accomodating their personalities, and are clearly being directed so that they get that down into English in a fluent and natural way. While there are differences, the changes are very much on message and in character, and they are expressing ideas in a fluent manner between languages. The official translation will also have been passed by quality control in Japan, who will want this translation to be good.
When you consider a fan translations credibility I would be looking at what they are choosing to change and the translators intents with these changes - especially if they are offering up a "more accurate" translation.
I study several languages and Japanese is probably the most toxic, and has the most difficult "community" surrounding it. This is mainly because of Otaku culture, which leads there to be a disproportionate amount of people coming into the language who aren't really into languages at all, they're into Japan, or anime. While thats not a bad thing, I promote the learning of languages, it does come with its own issues. Such as, not understanding how to properly express ideas between languages, and a resistancy to proper inter-language expression despite this being a fundamental skill for being able to fluently communicate ideas between languages.
Its a pretty important thing; its not all about syntax, and isn't all about "purity" in how another language speaks. This desire to strip translations away into something more "pure" is a dictinctively Japanese entertainment media thing to do. I don't see this happening much with Spanish or French. Not just because they're more similar to English, but because it doesn't have this same culture surrounding it.
To make a point, my GF is from Mexico, shes a law student at a presitgious university who is planning to do a masters next year, her major is international law, one of the roles of her mandatory internship involves the analysis of legal documents between languages and consulting on them. She speaks Spanish (native), English, French and Chinese. Needless to say, her English is obviously at a very high level.
She frequently however comes out with utter nonsense in English, or very confused statements while trying to put ideas from Spanish over into English. Particularly when shes trying to express directly from one language to another. As the common saying goes, you've got to think and express ideas in the language you're speaking, not the language you're interpreting from.
I bring this up because only today we had a discussion about joven. Its a common term in Spanish speaking countries for young. For various reasons they often use "adult" as the contrast to it rather than "old". There is a certain "Spanish way of speaking", which can be difficult to shake. Unfortunately it often leads to rather odd ways of speaking in English if you're not fully familiar with how the two languages express ideas differently. Sometimes it leads to rather amusing statements, or even inflammatory claims. Such as implying that you were the only child at the party despite being an adult. Or being in a conversation where you've just implied that your friends sister is a child bride and while this can work sometimes is ill advised, exclaiming that the pub is full of children, or the time when she implied that one of her friends... pardon?
It can also lead to unintended insults, such as accidentially inferring that an adult is immature, is like a child, or accidentally calling someone old.
So, these problems even affect the fluent, and languages are far more complex animals than being able to translate some words.
Pretty much, 90% of the time, these fan translation efforts for Japanese content that tries to be pure neglect the importance of expressing ideas in a natural way, and that languages don't work like that. These translations often spew out English that is akin to what happens when I speak to a beginner in Spanish, my GF's dad (he speaks very little English), or how I sounded when I was trying to talk to her brother in law in Spanish.
In other words, not fluent and not expressing ideas clearly or with the nuance I or they intend.
Watching that video I'm seeing a lot of translation into awkward English, petty translation changes (destinys crossroads into the crossroad of destiny), and there are times a character is saying something, they've gone super literal and the official translation sounds more knowing of whats actually being expressed.
I'm not going to claim to be able to give a precise translation argument myself, because I have patchy understanding of the scene. My Japanese is around intermediate level and I know my limitations. Also, as many people find, their ability to read and write is at a different level to their ability to listen and speak. To my ear though, the official translation *sounds* like what Aerith is saying, and theirs seems like a slightly ham fisted, simplified, Japanified, way of saying something similar. The kind of thing you get when someone isn't fluent in English or the language they're trying to speak in.
This is typically happens because they don't appreciate how language works, or they are unable to understand or express the nuance required.
Things such as Tifa saying ここには何がある stick out to me, which the official translation gives as "what will we find on the other side?", they've changed this to "whats beyond there?" which is the most literal and basic translation you might find of that sentence. That is a big red flag though, because this is a construction that comes up on places like HelloTalk, and other language discussion groups, all the bloody time and trips people up because there is stuff going on with that... some of that stuff might be confusing or invisible even to people who are aware of whats going on with it.
https://japanese.stackexchange.com/questions/1096/what-is-the-difference-between-に-and-には
Thats just one discussion on the construction and it doesn't cover the entire topic. I think, that maybe, the official translation is accurate and theirs is borked.
So, with that all said, to answer your question about whether its an accurate fan translation, I would say to go with the official translation for the reasons listed above. Namely that it sounds like an elementary level speakers translation, and it ignores how expressing ideas between languages actually work. If I find translations in any language that sound awkward, cumbersome, and lack fluency of expression, I approach it with scepticism. If I find translations that are trying to correct official translations by being more pure, and fall into awkward sounding expression or petty changes, I approach it with scepticism.
Also, what
@Makoeyes987 pointed out is also true.
