The way I did it was to just over-write the text in the structures, after game loaded up the data, I was able to load a csv for example and replace the item, npc, monster, quest, skill texts etc inside their structures. It was simple but got the job done.
If you find the text in memory for what it says, you can figure out the structure or at least the location/pointer to it, and the size of structure, then its just an array you can copy the string/bytes over what is there so long as it is within the fixed size constraints of those strings.
Of course you could go another way about it, detour the code that grabs the text for a particular thing you want to translate, then return w/e string you want.
If you look for where it reads the files from disk you can find a long routine of call something, if it failed to load push an error/continue loading next thing if I recall. you can also find the filename in memory inside those functions.
If you were to detour that function you could write code to run after it runs to then replace the contents for example.
I think I did it without a detour, just waited to know what screen it was at looking at the screen pointer, then loaded the info I wanted over top of the existing loaded structs.
There are newer tools than when I started doing this like ReClass.NET
which can help you map out structures a little bit nicer than working with the structure mapper in Cheat Engine to be sure.
Using Ida Pro or Hexrays or x86dbg
etc is pretty technical, but if you keep at it and learn things bit by bit you can start to make sense of things and it clicks.
By decompiling the assembly into C++ or something using HexRays or Snowflake or w/e it was called, you can more easily understand what the code does in some cases, but its still a wild goose chase if you don't figure things out and name them or look for strings or debug symbols. It's a big puzzle if your looking at the code/assembler for a compiled thing as you often wont have any nicely named variables and structures can be a bit of a mess.
Try to find the parts that load the text from the *.IMG files then find a pointer for that memory location.
You could also try putting mouse over an item and using hotkeys in CE to search for
Unknown 4 byte
Mouse over item, use hot key to search for (changed value, unchanged value) move mouse off item to not select anything, search for changed value, rinse and repeat.
If the value of a hovered item is stored in a memory structure, you might find it that way.
Then you can look for what writes this value/reads this value and find the code that uses it.
But since you know the name of the item and the name of files loading that info, searching it is much much easier tbh.
