First of all, let me correct that NC West covers North-America and Europe.
I've only been on Blade & Soul for 7+ months, so pardon me if I'm unaware of all the things the game has to offer, but I was thinking about investigating if we could localize these videos a few days ago! I've seen videos like these twice before. Here's something interesting for you: this is a lot of work. I've worked on similar projects for a different game before.
Someone needs to get the video project file (assuming we can get all the files and they're usable; oh a quick note that it can take just a few days to figure out how to transfer this huge amount of files). We then need to extract the text so we can localize it. The audio VO is probably going away because of the cost and time it takes to get the VO script (unless we can get it), localize it, and get a VO actor. It's possible but unlikely. Then we need a video editor to put all the pieces together, and this is the time-consuming part. Add some QA on top of that and a possible review that requires some modifications (in the worst case). And I'm not even factoring German and French into this mix, as it would increase the project's scope too much. Bear in mind that all this time and money is not used to do other things, such as build assets to promote a release. It is worth the financial and time cost if it allows many more players to play the content!
One last thought: would such a video push players not to try to figure out the boss mechanics? Part of playing video games is about solving puzzles, not just the picture that the puzzle shows you. And maybe the answer to this question is to release the video a few months after the dungeon's release.