Just a tip. To edit the text in the rom you:
Assuming the text is uncompressed (I think GBA Pocket Monsters game are)
Use relative search tool (monkeymoore, or CUE's RSEARCH) to make a tbl file
Open the ROM with a hex editor with table support (WindHex)
Normally you can find text and edit it with the hex editor at this stage.
However you're stuck with the original text length, which you can't exceed.
In case your text is longer, some people would use then the German/French script since it's longer, but...
The proper way would be to modify pointers. Hex data telling the game where the text begins. To do so:
Confirm the address where a given piece of the text begins, then look for pointers. (for GBA games, pointers are like this
-with rare exceptions-)
Once you locate pointers, you can use a "script extractor/insertor" utility (look it up in Utilities here, like Cartographer/Atlas) so that the game gives you a nice text dump. Preferably, you'd want to expand the rom (look it up) and make the pointers point there instead and the text inserted there.
You get a giant txt file with all data in-game, which you can modify as you like just with those frontends. And you can take breaks and save the work-in-progress document too.
Then you let the script insertors do their magic with hex editors and pointers.
Now, about that Advance Tool?
It just does the above. Nothing more.
But with some coat of shiny paint. And only for specific regions of a specific set of games.
It's by no means essential either.
And in this case, it made my browser throw up a malware alert, so it's not advisable.
tl;dr: do things the proper way. By the way, "my method" works with almost everything you want to alter its text (as long as it's not graphical text)