What is "best" is relative. I do not think changing dialogue to the point where it almost changes characters is "best".
Here's an example:
https://mangadex.org/chapter/93098b40-f34c-4f64-8599-689418ea536c/46
I agree 100%, that's bad localization because they didn't convey the
tone well.
And if you are going to have one-liners that are an integral to the person's character, why would you change or remove it?
Would you prefer it just be left in Japanese? Go read the source if you are that concerned about keeping the lines exactly the same
You did it yourself: "keikaku means plan" or "keikaku=plan"
Why bother reading a translation if you don't want things translated?
If your goal isn't the most enjoyable reading experience but rather solely source accuracy, passion and an hour a day will get you to an okay reading level very quickly so long as you have a decent memory, there's plenty of guides.
And you can skip all the annoying listening and speaking parts I still am slow at after almost 10 years due to spending very limited time actually speaking conversationally.
I can give some recommendations of materials I wish I had when I learned.
I just prefer localizations keep things like certain things like "onii-chan" and "sempai", rather than translating them into "older brother" and "elder student".
I strongly prefer honorifics, but they really aren't necessary.
"onii" can easily be changed to "bro" or just removed as English is more often written without the subject than Japanese is.
Senpai can usually be removed, but is often used exclamatorily so you gotta replace it based on context.
I do want to make clear that my goal was to convey that localization is difficult in a different way than fan translation is, and they have much different goals.
As someone who started by doing fan translations of light novels, my goal was to make something that me and other light novel fans would enjoy, at the time it was a lot more niche than it is now, so most LN readers were pretty diehard japan media nerds, so it was definitely a "make the text readable in English" type of deal, terms without direct translations were left alone.
Moving to localization changed that to making something that any fantasy fans would enjoy. Instead of making Japanese text readable in English, I had to make it into actual English text, the goal is to have it in a bookstore on the same shelf as other fantasy series', it should have the same knowledge barrier to entry so honorifics get cut.
A dedicated fan/group will usually be more enjoyable for me than anything official due to their love and lack of corporate restraints, and honestly piracy of translations are easier than of the raws...
I still have an issue with certain large groups who translate series on here and can't even keep names consistent for 2 chapters, they need more love!
Anyways, I spent a good while formulating this comment lol.
Sorry that it's a big long wall of text, but to be fair-- I worked on novels, not manga.