Do you have to speak perfect Japanese to naturalize?

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Perfect Japanese? Not at all. But a certain level of Japanese proficiency is expected.

The best explanations I was able to find were on the home pages of law offices, not on the 法務省 {hōmukyoku} (Ministry of Justice) website itself. If you are interested, a Google search for 帰化条件 {kika jōken}　日本語能力 {nihongo nōryoku} (criteria for naturalization, Japanese language ability) will give you a couple of pages full. However, none of the details I was able to find come directly from the Japanese government itself.

The general consensus seems to be that a Japanese level equivalent to 小学校 {shōgakkō}低学年 {teigakunen} (the "lower grades" of elementary school, or around a third grade level) is required and expected of anyone hoping to naturalize. But what does that mean in a practical sense? Most third graders I know can rattle off the rules to their favorite sport, or tell a decent story set in a fantasy world, or extol the virtues of the latest boy band in perfect Japanese. Most adult foreign language-learners, on the other hand, may not be able to do any of those things, but rather start by learning words and phrases appropriate for international business, or politics, or language teaching, or whatever their own career or field of study requires. The powers that be obviously don't expect us to speak exactly like a third grader, just at an "equivalent level."　　If you're curious, here are the third-grade 漢字 {kanji}, although you shouldn't feel hopeless if you can't write them all from memory - I can't either, and I was accepted. Being able to understand and pronounce them in the context of words and sentences encountered in daily life is probably fine.

While I have heard second- or third-hand stories of applicants being made to take reading and writing tests at the 法務局 {hōmukyoku} (Legal Affairs Office), in my case it was simply a matter of talking to my case worker in Japanese, filling out the paperwork in my own words and handwriting, and submitting a copy of my four-year-old 日本語能力試験2級 {nihongo nōryoku shiken ni-kyū} (Japanese Language Proficiency Test, Level 2) result. That apparently was enough, although I get the strong impression that this - like so many other things - is a case-by-case basis.

The best advice I can give is first, to ask yourself these questions:

1. Do I speak enough Japanese to get by if I ever had to live outside of Tokyo, Osaka, or another big city with a large English-speaking population?
2. Do I speak enough Japanese that I could take care of myself and my family in most if not all aspects of our daily life, without the help of my Japanese spouse or in-laws if it became necessary?
3. Do I read and write enough Japanese to fill out all the paperwork that needs to be filled out at city hall now and then?
4. Do I speak, read, and write enough Japanese that I could work the register at McDonald's if it were the only option to feed my family?

If your answer to all of the above questions was "yes," then you probably qualify. Now, the goal is to show your case worker that you are serious about naturalizing. They're not asking for anything that an adult with an average IQ can't do with a little patience and hard work - chances are, half of the reason for this requirement is just to test you: if you're really serious about wanting to live here forever, putting in a little extra time to study shouldn't be a big deal, right?

There are no real written guidelines for this, but a few common-sense recommendations:

1. Speak Japanese, and only Japanese, to your case worker and anyone else you encounter at the　法務局hōmukyoku （Legal Affairs Office）. Don't expect them to accommodate you in English or any other language.
2. Remember the basics before you go in. This should be a no-brainer, but if you can't fill out the 住所jūsho (address) line, or your own children's names without consulting your 携帯keitai (cell phone), that may raise a red flag.
3. Fill out your own forms and translate your own paperwork as far as possible. The only thing that you are required to write in your own handwriting (although they obviously have no way of knowing if you actually composed it yourself) is the 動機書dōkisho　(statement of intent?), but if it's your own name listed as 翻訳者honyakusha (translator) of all of those overseas documents, it can only be a point in your favor as far as language ability goes.
4. Practice for your 面談mendan (interview). They'll ask about things like your work, studies, marriage - any major events that have happened since you came to Japan. If your spouse is Japanese, they will interview you both about where you met, when you met each other's families for the first time, whether or not you know each other's siblings, even who were the 証人shōnin (witnesses) when you were married, so practicing giving the same personal history, in Japanese, can only help you there.

If that still doesn't give you a good idea of what is expected, there are plenty of naturalized citizens on YouTube to inspire your Japanese studies. Check out:有道出人 {ARUDŌ Debito}　(ARUDOU Debito) ラモス瑠偉 {RAMOSU Rui} (RAMOS Rui), Konishiki, ボビー　オルゴン {Bobī ORUGON} (Bobby OLUGUN). All naturalized citizens... how good is their Japanese? (Better than mine, IMHO!) See for yourself!