Q:

How do I help my wife control her irritablness and anger so she doesn't induce me to a rage?

My wife is very irritable.  The slightest annoyance can make her stern, change the way she speaks, and cause her to increase the volume and pitch of her voice, and essentially hammer her point to somebody until they are subdued into silence.  I see this behaviour with both her parents, her grandmother, and myself.  I don't think she behaves this way in the workplace or with friends although I'm obviously not always with her.  But I doubt that she is like this with other people because she is very sociable, a great networker and has many friends.
When she speaks with her parents she is likely to get angry whenever they don't understand something, make a mistake, or disagree with something she is doing.  She will raise her voice and keep speaking louder and faster, and argue with them until they are subdued.  Her father generally just makes his point but quickly gives and goes silent; her mother is more argumentative and will also shout back and they will have full-blown arguments until her mother just goes to another room, slams the door and hides away for a while.
She is not particularly aggressive to her grandmother who is an old lady but I've noticed that even with her while her voice doesn't tend to become shouty my wife will increase the pitch of her voice and consistently hammer away her point to her if they disagree on something (maybe her grandmother disagreed with how my wife spoke to her father for example).
My wife has told me that during her childhood her parents were extremely argumentative and couldn't get along so they were regularly fighting; they have not lived together for 20 years and they've tended to argue easily whenever they are together to the point where they now just don't speak to each other at all, even if they are in the same room for 4 or more hours at at time.
We've been together many years and married a few, and she has always been somewhat irritable and easily angered (except for the first year we were together).  I'm fairly good natured and have generally just accepted it as her part of her personality and let things slide, just nod along, do whatever she wanted done at the moment, said 'sorry' and 'it was me who did wrong' and whatever else would get her to calm down quickly.  I feel I learnt a long time ago that arguing back was fruitless so just found methods to return her back to a normal state as quickly as possible.
In many ways we are happy and we are financially stable with no real worries at all; we have jobs we generally enjoy, reasonable salaries, have a home with a mortgage, no children and no health issues so there is no obvious underlying issue that should be causing my wife to be so angry and irritable.  My wife is also generally very caring, has helped me a lot while I studied while working, and we often have a lot of fun together.
But things my wife was angry over with me include: I didn't turn the light off on the landing (many times); I'm late to meet her by 5 minutes (although she is also just as often later, and sometimes by a lot more, and I just laugh); I didn't send her a text to ask her how she felt at a particular time of day; my sister was late to meet us by twenty minutes; I invited a good old friend to stay with us at one weekend at a yet-to-be-determined time in the future; I went for a walk (after telling her) which lasted a couple of hours longer than I expected and when she phoned me I didn't answer for the first couple of calls as I was walking and didn't hear / feel the phone.
Any of these things have made her angry; this can result in being berated from a couple of minutes to an hour or more and I have to pretty much agree that 'it's all my fault' and say sorry multiple times to get her back to normal.  Many of these things I wouldn't even think of if she does it, or will just laugh as she realises her double standard (and she'll laugh too when she's caught out, such as being late).  Some aren't even really my fault, like my sister being a bit late, but I still have to say it's my fault for not considering and planning for my sister being late.
Anyway, despite my attempts to generally humour my wife's moods, on two occasions she drove me to an extreme rage.
The first time I don't remember why she was angry with me; it was unlikely to be anything serious because in many many years I've not done anything that a reasonable person would think was very bad.  That time she was smacking me across my arms; she was not hitting me so hard that I would be really hurt by it but it was repetitive and it was hard enough to hurt a little and be somewhat uncomfortable.  Along with the stress of being shouted at and berated too I felt extremely uncomfortable.  I eventually reacted by screaming in her face repeatedly to 'never hit me again'.  I was screaming as loud as I could and very close to her face and continued until her mum came to see what was wrong; at which point I told her that my wife had been hitting me and so I left the room and went to spend some time on my own.  My wife was silent when I screamed at her; she seemed intimidated by me and didn't shout back; I think she was shocked that I change and release my anger like that.
I should say that she has never repeated that slapping behaviour since that day and I think she's clear now that I find it totally unacceptable. It wasn't a regular thing before that although I don't think that was a one-off event, it may have happened once or twice before.
The second time I raged at her was recently and she started raising her voice and berating me because I made a comment that upset her; this time it was a mistake on my part, because I insinuated she had bad feelings towards my family, but really, the way she spoke led me to believe she was making a point about them because she ended one conversation about money and switched immediately to them (not that money and them is a big issue in any way).
Now, earlier that week she had already come home one evening and berated me for an hour where I said nothing and just took her shouting and ranting and did my best to calm  her down; the reason was because I hadn't emailed her to see how a medical appointment for a very minor issue had gone (her mum had already updated me and she was due home in 30 minutes so there didn't seem much reason to do anything but wait).  Later I'd let her know how much it upset me and that I felt it was actually a bit abusive and she was very apologetic for a couple of days.
So when she started berating me again I first stayed quiet for about 5 minutes and just listened to what she said, hoping she would just finish venting. But she then started asking me questions so that I couldn't just be silent.  I told her I was sorry but she continued shouting, so then I told her 'it was all my fault and I was wrong' but again she continued going at me. I suddenly started to feel angry and told her to stop what she was doing; she didn't so then I said it more sternly and also swore at her; she then complained that I swore at her and continued complaining at me.  Suddenly I felt the anger increasing rapidly and kept repeating 'stop shouting at me' with variations increasingly louder until I was screaming at the side of her face while she sat there looking away in silence. This only last about 10 seconds and then I got up and walked away to be alone while her mum came to see what was happening.  It was even worse than just shouting because I'd been eating when she made me angry and I accidentally also spat out food that was in my mouth and throat while screaming at her so that it was on her hair and clothes.
I've haven't spoken to her since although I have spoken to her mum.  Obviously I apologized to her mum but also told her that I was struggling to cope with my wife's short temper.  Her mum of course was upset with my behaviour but she was pretty understanding too because she can really empathize; she actually is at the end of my wife's short temper much more often than I am.  I used to try and reign my wife in when they argued but gave up long ago as that would just turn my wife's anger towards me.
So I have to make peace with my wife again soon and I know we'll both be very sorry, but I also think that she is very much likely to continue being short-tempered and resorting to angry behaviour. I would like advice to help me and the rest of her family both cope with this and help her find better ways to cope with irritation, annoyance, etc.
I don't want to feel that rage again; I don't want to behave like that; I try my best everyday to be a friendly and helpful person with everyone I meet and interact with, and have arranged my life to deal with negative people as little as possible (especially those from my past who would cause me to feel angry).  During some low points in my life I've suffered depression and had suicidal thoughts so I really value a calm and happy lifestyle.  I think because I've been in those negative states before I've learnt to not let little things annoy me in the same way my wife has, and I also don't have high expectations of everyone and am fairly understanding of people's minor failings.
For some background, my wife is Chinese and I'm British, and we live in the UK; she has lived here much more than a decade and is fluent English speaker, has a good job, and is as integrated into the culture here as she wants to be.  Her mother comes to visit every year for a few months.
What steps can I take to help my wife deal with her irritableness and anger so that I'm not in a situation again where I enter a rage?

A:

I went through something somewhat similar when I was married. My partner would get upset or stressed and would resort to shouting and berating the people who were closest to them. Their parents, children, and me. A simple apology was rarely enough to sate the tantrums, they seemed to need a full groveling submission before letting up.
I'd like to tell you that I figured out a way to help them channel their anger more appropriately, but that would be an overstatement. I did however find a way to deal with it until they decided to seek professional help. 
I ended up using a series of what I call "meta discussions". I'd wait until the storm had passed and everyone had a chance to calm down, and then have a talk about how we talk to eachother. It wasn't a rehash of the fight, but instead talking about how we fought. Through these discussions I learned a lot about why they behaved that way, mostly that that was the way their parents fought. 
Eventually I learned that I didn't have to put up with being treated like that. When they started shouting, I could just calmly make my exit and return home when they'd run out of steam. We discussed this approach in a few meta discussions and decided that it was probably for the best... In the heat of the moment, when emotions were high and they tried to keep me home and force me to listen to the shouting, I learned to say:

I don't deserve to be treated this way. When you're ready to talk to me like a partner, we'll talk.

This helped me keep my sanity till they sought out professional help. This is not a complete solution. The complete solution really does require professional help and support.
Also, I'm in the process of getting divorced,  so take this with a heaping spoonful of salt ;)

