1. The locals stop praising your Japanese.

It’s rather patronising — if you string together a semi-coherent sentence, if you manage a couple of words, you’ll be told 日本語はお上手ですね, nihongo wa sogoi o-jozu desu ne, isn’t your Japanese ever so good? The Japanese woman — it does, for some reason, seem to be women who’re more prone to this behaviour — who does this might not actually muss up your hair or squeeze your cheek, but the condescension’s unmistakeable.

Japanese isn’t a terribly hard language to get started with — the grammar’s pleasingly simple, there are no irregular verbs (or only two, depending on who you ask), there’s none of that tonal nonsense that so bogs down learners of the various forms of Chinese. So it won’t take long before you can actually put a meaningful sentence together, and, as your Japanese goes beyond the phrase-book basics and you start your adventures in syntax, the compliments dry up really, really quickly.

As you start to tiptoe through the minefield of Japanese sociolinguistics, trying to figure out which of the half dozen or more words for I you should be using — 僕 (boku) when you’re talking to colleagues, 俺 (ore) if you’re down in the pub, 私 (watakushi) if you’re giving a speech, 私 (watashi) any time you’re a woman, just for starters — you’ll find the praise much thinner on the ground. I’m not totally sure what lies behind this, but I suspect the Japanese are very possessive and protective of their language, and they slightly resent foreigners using it.

There is, at the other end of this phenomenon, a belief that Japanese is an impossibly difficult language for foreigners to learn. While it’s true the writing system, arcane beyond comprehension, is ferociously complex and impenetrable (I was very proud to have, after a decade there, achieved a reading age of about 11; if you don’t believe how messy it is, just note how watashi and watakushi are both written 私), the language is no more inherently difficult to learn to speak than any other.

But there’s an entire body of, if we’re using the word loosely and generously, scholarship, nihonjinron, the study of the Japanese people, that’ll try to tell you Japanese is processed on the other side of the brain from other languages. This is, of course, utter bollocks — to the best of my knowledge, no neuroscientist has found any evidence to back this up — but I strongly suspect the surprise many Japanese seem to experience when they hear me speak reasonably fluent Japanese is rooted in utter confusion.

2. You invite your mates to have a bath with you.

Bathing is a pastime in Japan, a leisure activity, an entirely communal practice that just happens to involve being totally naked. I lived for two years in Shimojo, a tiny farming village of 4,000 souls in the southern end of Nagano Prefecture, an hour and a half northeast of Nagoya, and during my time there I became a regular at コズモスの湯, Kozumosu no Yu, the local hot-spring baths.

I was invited by students in my adult-education evening classes and grew to relish the experience, especially in the winter when the Southern Alps were buried under snow, and the steam rose up from the 露天風呂, the rotenburo, the open-air pools. You’ve no doubt read the standard description — shower yourself down first, get the soap off yourself, sit in the hot water — but until you’ve tried it, you can’t truly understand how relaxing it can be. The heat — the water’s so bloody hot you can barely stand to move — soothes your aching bones deeply and powerfully.

So when friends came from the big city to visit me, I’d take them to the bathhouse after dinner. This was normal. And friends invariably came with me. The ladies would bathe with my lady friend. The men would join me in the hot water of the male bath, and we’d buy a couple of bottles of beer and slowly cook. It was a sublimely wonderful experience; oddly, then, I’ve asked no one, since I’ve lived in New Zealand, to have a bath with me.

3. You have a clearly stated preference for beer brands.

There are four nationally marketed brands of beer. Sapporo, Asahi, and Kirin are quite excellent brews; Suntory, on the other hand, is what you drink when there’s nothing else available. One night I was out with Richard at a つぼ八 (Tsubohachi is one of the country’s main chains of 居酒屋, izakaya, the pubs that serve cold beer and fried deliciousnesses), and they were serving that particular evening only Suntory’s summer brew.

Richard, now, is a New Zealander — there are few that can drink as well as my Irish cousins, but the Kiwis are right up there — and when he was served his 大ジョッキ (a daijokki is the largest size of beer glass, usually a pint or more) of Suntory Summer Beer, he took a large gulp, put the glass back down on the table, thought for a moment, and said, “Let’s find a different bar.” I tasted my beer; I agreed. I’ve never seen a Kiwi leave a beer before, or since, but that night even Richard couldn’t choke down his Suntory.

It’s not good beer, thin and watery usually, but when they do their limited-run special brews, it tastes like someone’s not quite cleaned the pipes out properly after last summer’s batch. I followed Rich out the door; we found another bar selling Sapporo.

When I could find it, Sapporo was always my beer of choice. Yebisu, their premium brand, was marketed as ちょっとぜいたくなビール, chotto zeitaku-na biiru, the slightly luxurious beer, and it was, indeed, just a little more expensive and just a little more full flavoured and richer than the competition.

4. You know where the all-night beer machines are.

Every “look how freaky Japan is” article mentions the 自動販売機, the jidohanbaiki, the vending machines that sell anything you could wish for, and plenty you wouldn’t, including cans of coffee — hot or cold, your choice — or corn chowder, or potted plants, or pornographic videos back when people still actually bought videotapes.

That last one I’ve actually seen, at the side of Highway 122 between Ota and Tatebayashi; I’m sure there were plenty more around the country. I’ve not seen, although it’s often trotted out in this context, the machines that sell schoolgirls’ used knickers — I clearly used to hang out in the wrong part of town.

But I did know where the beer machines were. Many off-licences have a bank of a half dozen or more vending machines outside them, the easier to pick up a couple of bottles of Yebisu on the way home. This is quite astonishingly convenient, especially since most off-licences would close around eight or nine in the evening. But the machines themselves are (at least they always were; I’ve not been back for a while, and things might possibly have changed by now) turned off at eleven and won’t come back on until five in the morning, so if you want a midnight beer you’re out of luck, but if you need to pick up a can of lager to pour on your cornflakes, you’re in business. I was told, but never managed to confirm, this law was to prevent underage alcohol purchases. How exactly this would work was never satisfactorily explained to me.

At least, that was what the law said. Every town would have one or two that would keep dispensing through the night, even if the lights were turned off. You knew you’d arrived, that you’d been accepted, when someone finally told you where they were.

In the early 2000s, a new development started to make the all-night beer machines less essential. Some beer machines were fitted with card readers that could pick up a date of birth from a driving licence. What a fantastic idea this was — the only people who could buy a beer were the ones who could drive home again after drinking it.

5. Your life revolves around trains.

Real-estate agents advertise flats in terms of how close they are to train stations — the closer they are to a station, especially a station on a JR line, the more you’ll be paying in rent. You’ll find yourself memorising, internalising, train timetables. You’ll know, instinctively, whether you have enough time for one last daijokki before the 最終電車, the saishudensha, the last train home, leaves. You’ll learn where to stand on the platform in the morning to have the best chance to get a seat on your morning commute. You’ll develop, without even realising it, the ability — the Japanese seem to be born with it — to sleep all the way up the line and then wake up just as your train arrives at your home station. It’s a quite remarkable talent.

After it passes Kita-Akabane, the Saikyo line continues north out of Tokyo for another 20 minutes before arriving in Omiya, and as it passes through the southern reaches of Saitama Prefecture, the towns and cities are utterly indistinguishable. I commuted from Omiya to Shinjuku, on and off, for nearly seven years, and even at the end I struggled to tell the difference between Toda and Urawa and Yono. The grey concrete and the turd-brown apartment blocks and the flashing neon of the pachinko parlours and the コンビニ, the konbini, the convenience stores, blurred into an endless mess of urban sprawl that carried on far beyond Omiya, up to Kuki, and most of the way to Higashimatsuyama and Hanyu.

I was reluctant at first to fall asleep, afraid I’d miss Omiya and find myself in Kawagoe with no idea of quite where I was, but one evening after a particularly strenuous day’s English teaching I dozed off a little north of Ikebukuro — I don’t remember reaching Jujo — and as we left Kita-Yono, as my train entered the tunnel under Omiya station, I sat upright and awake.

It had finally happened. I had, very slightly but very really, turned Japanese.