Can’t save changes in core.lvl (english.locl) — how to properly localize SWBF2

[KASPER01]

Hello.

I want to localize Star Wars Battlefront II (2005) into my own language.

I tried to edit the game text through core.lvl, but I'm stuck.

What I did:
Opened core.lvl using LVLTool
Found the localization file english.locl
Edited the text (translated it)
Problem:

LVLTool does not properly save the changes.

After editing:

either the file doesn't actually save
or it saves but nothing inside changes
or changes are simply not applied

So basically I cannot get a modified core.lvl with my translation.

Questions:
Is it actually possible to edit english.locl inside core.lvl using LVLTool?
Is LVLTool only for viewing and not for proper editing?
What is the correct way to change localization in this game?
Do I need to use Mod Tools and rebuild (munge) a new .lvl file instead?
Where can I get proper source localization files (not VarBinary)?
Goal:

I want to translate:

menu (Instant Action, Options, etc.)
UI
general in-game text

If anyone has:

a working method
example files
or a step-by-step guide

please share.

Thanks.