I wanted to edit the notepad++ lua file but changes that I make on the file doesn’t reflect on notepad++

If you want to just add keywords, just use the Style Configurator … it’s easier that way.

if you insist on editing the config file manually, you need to understand and follow the sequence in https://npp-user-manual.org/docs/config-files/#editing-configuration-files, or use a different editor to edit the config file (while Notepad++ is not running).

Sorry, I know nothing about Lua or the Roblox variant, so I don’t know what you think is wrong with that image. And, as I said, the UDL system was designed for basic highlighting, and wasn’t designed for the complex, nuanced cases often handled by full dedicated lexers.

Personally, if I were wanting syntax highlighting that was based on Lua, I would just add User Defined keywords to the INSTRUCTION WORD and FUNC1,FUNC2,FUNC3 keyword types in Lua’s Style Configurator section, and not worry about the keywords that Roblox “removed a lot of stuff from Lua”

Is there any other program your recommend me to use, maybe you can’t say it but I would like to know. I want a program that has something like notepad++ has, I need custom syntax highlighting.

I want to make it so it behaves exactly like the original Lua syntax that has notepad++

That’s not going to happen. UDL was not designed to give you all the subtle nuances of a full-blown lexer; it was provided as an alternative for people who don’t want to learn how to program a lexer/plugin.

There is a huge lack of documentation on UDL

Wow. I feel exactly the opposite. The npp-user-manual.org’s UDL page gives an good overview, and that manual and the UDL dialog itself both link to the excellent, long-standing detailed UDL reference provided by Ivan Radić.