Backporting a script depends upon the game.
Sometimes it is essentially doing the translation again (all the pointers, all the fiddling with fonts/encodings, all the everything else) but likely not having to go find a translator as the script should be all there in the same order. Other times it can amount to copy and paste the script files (maybe also the font) like so many undubs, but for text in this instance. Japanese games tend not to have all the niceties for Roman alphabet using languages and such things tend to be added in by the localisation teams but in recent years they have been getting better about it.
Be careful when you say script to ROM hacking types. It can mean one of three things
1) For most purposes it will probably mean the game's text. As in film script, radio script, play script...
2) Events within a game being dictated by a scripting language used by the game, either a high level one used in PC coding (several DS games are coded in Lua for instance) or something a bit more specific to the game - I once decoded one for a game called Riz Zowad/Wizard of Oz - Beyond the Yellow Brick Road that had basically the entire game in scripting form for its own custom script. Not all games will have this and some will just have any events that happen be plain old code called when it needs to do it from within the binary itself, for others it will be a part of the level data and others can have other approaches with it buried. In general game parlance a scripted event is an event that happens within the game that was compelled to happen by the programmers (probably every time), however in reality if you are looking as a ROM hacker there are many rather minor scripted events.
3) Just to be fun scripting/scripters in pokemon deals with the events the game throws at you and things that happen. As pokemon tends to be a highly hacked game this is more of a high level skill like level design for the purposes of pokemon hacking.