YOU dont need it, I get it, so its okay, but please dont talk for the majority:)
And, likewise, you should follow your own advice.
I can see how multilingual chapter names could have use for some people. The question is, how many people edit their chapter names? How many DVDs and BDs come with chapter names more complex than "Chapter 01"? I know some that do; I own some, which are multiple-language. And they have the chapter titles available in (wait for it) ONE language. Sometimes it's English, sometimes it's Japanese, Chinese, I even have one title with the titles in German (disks bought from German market).
Would this feature be
generally useful? Enough so to increase the complexity of MakeMKV to add an XML editor? Will it speed up the work flow for those needing it, as opposed to using a tool designed for the task?
The same arguments apply to "Why use MakeMKV when Handbrake can be configured to rip the files from the disk AND transcode them to a more compact encoding in one step?" If you rip one disk per day, it's certainly more convenient to do everything in one tool. Do a dozen or more a day, not so much.... Best tool for each job.
When you are coding something yourself, you only have to convince yourself that a feature is useful. When you're asking someone else to do it, you need to sell the idea, to show why it is important or desirable for that person to do the work necessary to add that feature.
What you've posted so far is an excellent explanation of what you are talking about, and why YOU want it. Time to convince others as to how useful it will be to THEM.