Pro tip "Please help" means nothing as it could be anything. Something like "Looking to translate Rhythm Tengoku into Brazillian Portuguese" would be far better.
I assume as we are in the GBA section you want to translate one of the GBA versions (there is a v1.1 version presumably with some bugfixes out there it looks like) rather than the DS or 3ds efforts. Either way it is a Japanese game rather than something else.
We have a guide to hacking in general, which would include how translation goes down, with a focus on the GBA and DS
https://gbatemp.net/threads/gbatemp-rom-hacking-documentation-project-new-2016-edition-out.73394/ , I did also send a copy to someone looking to translate it to Brazilian Portuguese the other week as well but that might be a while yet.
https://www.romhacking.net/start/ is also good stuff.
Usual workflow is you will want to find the text, the pointers for it, any markup in the text you might need to handle, probably the font as I doubt it has all the various accents and it would not be surprising to see it lack a nice Roman alphabet.
Have you done any of this yet?
There is an existing translation (albeit classed as beta it seems) on
https://www.romhacking.net/translations/1762/ and
https://github.com/ShaffySwitcher/RhythmTengokuENPatch so you could look to see what was changed for that as it will likely also apply to this, there is also reference to various servers and wikis that might have more info.
There are Brazilian hacking sites
https://www.romhacking.net.br/ being the present home I believe of a far older community (
http://romhacking.trd.br/ is what it was but it went some years ago now and I lost track of it). A lot of people doing very good work there; I have found more advanced versions of tools made for it which is usually a sign of good things.