So I don't really think I can help you as my experience with NDS hacking is pretty much zilch, but I do know a fair bit about text encodings. I'm a tad confused because your question doesn't make a ton of sense.
UTF-8 can encode literally anything that can be represented as text. You shouldn't need to turn it off (or even really want to? It's kind of the universal standard).
An encoding clash between the editor and the game is likely, but if you're only using an English characters for the text, those should show up in any encoding, as the basic ASCII set is pretty universal across all text encodings. So if that's a problem then there's probably something else going on.
if this particular game does things the "old" way, it might have it's own glyphs among the graphics that need to be changed with a tile editor .. and the text may not conform to ANY standard encoding system, in which case you'll need to use a table file to translate your text into the proper encoding. This is how older games did it, and you can find a bunch of docs on this site about how to create and use table files --- however I would be surprised if games into the NDS era still did that so I don't know how likely this is.
That's about all I got. I guess the first thing I would recommend is try to figure out the actual encoding that your text needs to be in. That is... what bytes correspond to what letters. It seems very unlikely to me that you're really using UTF-8 if you're running into these problems.
AH! Another possibility is that the game is using UTF-16 and you are putting your text in as UTF-8 or ASCII. I don't know if this would quite overlap the kanji area of UTF-16, but it's a thought!
Like I say, figure out what the game needs first. Figure out how to configure your tools once you know what the game is using.
I also didn't realize I was in the newbie forum. XD Sorry if my answer is a bit intimidating. I don't normally hang out here. Hopefully you get the jist of what I'm saying. If not feel free to ask questions and I'll try my best to answer. I don't want to scare you off.
, I'm not a native english speaker, so, excuse me if sometimes my english is garbage.
Now that I read the title again, it doesn't make sense, I should have put ''How to get rid of multibyte characters on text (NDS)'', it's clear that I need my 8 hours of sleep before posting XD.
Going back to the game, this game in particular has a basic roman alphabet (standard letters and numbers, but not variations like á ä, ñ and such, for writing on romaji, I guess?) coded, alongside two japanese writing systems (kana and kanji, the first used on both menus and editable objects, and the last only is used on menus), but knowing that this is more a toolkit for game making than a ''game'' itself, its likely that the roman characters will only be able to be used on editable objects, and not on the menus, I'll check out the text encoding, just to make sure I'm not using the wrong one, but seriously, how one can get rid of multibyte characters?
I'll consider that maybe the menu text its written on tiled images *flashbacks of when I was editing menu tiles on Fire emblem 7 for the first time*
, It should be easy to see on a nds image viewer.
I need to investigate further with file managers/viewers, I'll post here any advances that I do if I get somewhere.