I am lost as to what you have and are trying to do with that info.
"03001690 (skip to intro with the value 04)"
Does this mean the game will not show the language select if it sees the value 4 there? Presumably for people doing a soft reset or having finished the game and being dumped back at things after the credits or exiting via a menu.
If so then you.
Or is it just a kind of page count as it were (we have done 0, 1, 2 and 3, now we are doing 4 sort of thing).
Or is it the language value selected for the game use (note, might be different to the one the game uses to determine language to display).
VBlankIntrWait is a BIOS function that makes the GBA go into a low power mode; there is nothing much happening on this screen so presumably the devs, or maybe compiler, put it in low power mode because it is good form while it awaits your command.https://www.coranac.com/tonc/text/swi.htm
has a bit more on such things if you wanted it.
... this is getting nowhere fast. I will try another approach.
Game intros are usually just slideshows. They will display a picture, maybe some music, maybe a fade, in some cases maybe a little animation too. Some will be individual code sections for each slide, some will be more of a slideshow loop (at end of slide one add one to counter, display next slide, if counter = [end slideshow value] then goto game). Sometimes this intro can also be a distraction if it is copying data or doing some long winded setup, though as the GBA is not a CD console, uses directly mapped fast memory and nobody does procedural generation at this level on the GBA this is not so common here.
Language (and in some older games then difficulty too) tend to amount to a thing to select the language, and a thing to set the language value/flag/variable once you press A/start/select... on your chosen language. This final language value need not be the same thing as the thing as it uses to remember where the cursor is presently located on the screen.
Your job would be to find the final value it uses. Fortunately it should be simple enough to find as nothing else has happened in the game yet to make the memory change too much. You would then do a cheat search after the language select happened (as in you selected one and pressed A or start or whatever and the next screen is happening) to see where it stores the value in memory (select either a different value and do a difference scan or the same value and do a same scan, mixing it up a bit should narrow it down, aka a fairly basic inventory item style cheat finding session). Outside chance it could be a register it keeps the value in but let us not get too silly. You might even already have this location. If you have the cursor value then you could go a bit more advanced with the debugging as it will presumably have to reference that after you press a button to confirm the selection.
When you pressed the button to confirm selection it will then go to the intro. You want to find out what location in the code it jumps to for this. A quick aside at this point to go back to the nature of intros above then if it is individual code sections then each will jump to the next section after they are done and skipping would involve changing where these jumps land.
I imagine the language screen will end something like read the controller input (or its debounced* location) and see if A/start/whatever it needs is pressed. If the relevant button has been pressed then set the language value in memory (if it is not already set) and eventually (don't know if it kicks in a fade or something) jump to the intro section. If it means you have to press next instruction a lot after confirming selection to eventually see where it jumps to then so be it.
*switches are either on or off but owing to the nature of physical things springing any given millisecond might be different to the previous despite ostensibly being pressed or depressed. Most games will copy the state of the keys at vblank, which happens 60 times a second, and do all their operations off this copy rather than risk having something strange happen if it is pressed for one thing and not a millisecond later when the next instruction reads it but the code reasonably assuming the previous thing happened.
Your job then would be to in the last logo screen before language select set the language value to what you want and force it to jump to the intro (which you have the location of). You might even be able to go even further back and do it essentially from boot. Technically you could also do it in the language selection bit if you wanted (might be easier if it is just a slideshow before)
It could quite easily be a two instruction change, one to store the language value you need, another to set a jump to the start of the intro.
As in whatever memory store command (the GBA/old school ARM processors have instructions to handle memory rather than things like X86 which do it directly in instructions) will do the deed followed by whatever jump you need to get to the placehttp://problemkaputt.de/gbatek.htm#armcpureference
That said do be aware of ARM and THUMB -- THUMB is basically a 16 bit instruction set which the GBA uses to increase the amount of code for a given amount of storage, it is not as wide ranging as ARM but can do most tasks well enough, especially intros to games. If it does switch (your debugger emulator will tell you what any given screen is operating in) then you will probably want to do the switch as well but that is just a single instruction.
If there is no space available (do bear in mind you have a whole screen you just bypassed and is not functionally irrelevant) then jump to a blank section of the ROM and do the deed there instead.
Finally if above I was right when I asked if that meant it skipped to the intro if it saw a value of 4 at 03001690 then even better. At some point in the logos or initial setup, basically somewhere before language select, simply throw a 4 into (a store memory command will do it) that location and the game will handle the rest.