We are heading down the "more art than science" parts of coding at this point, though choice phrase tends to be "falling debris" (as in watch for it). This is also ignoring that localisation need not be just changing text around (maybe changing script to appeal to the imaginary local kids as well) and can include bug fixes, rebalancing (which can include harder) and censorship things.
I am not sure where to start with this one.
Bug fixing, including "it is 5pm on a Friday and I want to go home" methods appear here. One that sticks was I think from a GDC talk where a guy was talking about his time making the Tron game that appeared alongside the film a few years back. They were using unreal or something and turned out a given item was invisible. Turns out in whatever version of unreal was used an item of a given number was forced invisible by the original base game bodging some code that was spun out into the engine. Solution from Unreal themselves was "don't worry, just make item number blah a basic cube or something knowing it will be invisible, don't use it in the game and go from there".
Still from a ROM hacking perspective there are two primary suspects if I was to investigate things.
1) Weird memory read issues.
Usually seen more in devices with bankswitching, especially if code was duplicated between areas as a safeguard that was skipped when either the translating company opted for a cheaper bank setup (or maybe just a different one) or did not immediately become apparent.
2) Timing issues.https://arstechnica.com/gaming/2011/08/accuracy-takes-power-one-mans-3ghz-quest-to-build-a-perfect-snes-emulator/
is probably one of the more noted examples of such a thing in games/emulation, and nicely covered. Comes in other forms as well https://hackaday.com/2015/10/26/killed-by-a-machine-the-therac-25/
More generally there is a reason why most instruction lists come with cycle times, DMA reads will have times associated with them and latency is a thing taught early in electrical engineering (though more likely to be called circuit hazard at that point).
1) and 2) can sort of combine as well, especially if the original devs did some kind of http://www.catb.org/jargon/html/story-of-mel.html
shenanigans and were all "ooh that text routine is this far away from my drop rate, let's use it to calculate a jump" and other sorts of things that leave us with https://www.loekalization.com/mistakes.html
type setups in more general discussions. Get enough of that and things still making it through play testing
If you are not familiar with coding errors in general then might want to sort that too if going to be going too much further into this sort of discussionhttps://textexpander.com/blog/the-7-most-common-types-of-errors-in-programming-and-how-to-avoid-them
(7 might be a few more than some try to categorise them as, few less than others). It is not anywhere near as arcane as some of the other links I have dropped so far either; it is often the sort of thing taught maybe not to day one codes but definitely first week.
I would also flank it with https://www.joelonsoftware.com/2010/01/26/why-testers/ https://www.joelonsoftware.com/2000/08/09/the-joel-test-12-steps-to-better-code/
as again it is really useful to know, even if you are not a coder (not to mention coders don't always make the best testers, and testers don't need to be coders).
and as far as "because I would like not to worry about one thing someone I commission does somehow modifying something else" then nothing you can do. Most times it won't be an issue as the way games are coded tends to mean things are fairly obvious and unlikely to happen owing to being isolated. Can go one further as well. I have all those links either in my bookmarks or found them first go in a search engine from memory, and would say I will pit my skills against any of those people, might not always win but it would be a proper fight for them. I can't be sure either outside of an insane degree of testing (and even then I probably have to worry about console manufacturing variances*) that nobody does, possibly even for the medical machines -- if you have ever been bored (even as someone that likes fiddling with things enough to be on a site like this) by good boy coders prattling on about testing oriented approaches to coding, unit testing, the importance of a good specification and the like then you have seen nothing yet for the sort of insanity required here. Though I will at least give them one the importance of good specifications; most professional failures and nightmare projects have been because I did not secure one or push for one. Given most localisation teams would be happy to have Japanese comments, never mind a nice full code listing, systems overview, coding philosophy and all that jazz, then... yeah.
More generally this is games. There will be bugs. Nobody will be hurt, fixing them might even be fun.
*actually a thing that has come up, and I can't wait for it to appear when FPGA stuff happens in a few years as those kinds of pedants are some of my favourite to wind up. Usual examples if you wanted them would be go look at the controversies surrounding gamecube pads in Smash brothers tournaments, and costs of some of those that happen to fall into the desired regime and also the original xbox and slow RAM (they were building them on the cheap and using RAM that might not have made the higher grades so some of the earlier models were slower than nominally the same devices in later batches/models, and this can have effects in games). Lesser versions for different clock speeds between devices with backwards compatibility (and failures thereof). Sort of related is also the floating point error in Wii emulated version of Super Mario 64 vs original, and comes up in certain speedruns/challenge runs as it allows some different techniques.
Couple of other links that are of passing relevance herehttps://trixter.oldskool.org/2015/04/07/8088-mph-we-break-all-your-emulators/ https://www.youtube.com/watch?v=fWqBmmPQP40
We have not even talked about malicious actors/trolls, covert anti piracy (some do like the challenges of the subtly break the game versions),