How long does it take to learn or be good in nihongo?

ok here's the deal: im 18yrs old and im planning to work in japan as a nurse by the time im 22... so how long does it take for me to learn their language? i know most common japanese words and im planning to hire a private tutor by Christmas.. and what are the most important or critical stuff that i should know?

That really depends on your determination. It is not one of the easiest languages to learn. What you can definitely do before getting here is learning the two alphabets Hiragana and Katakana. There are books and online resources to support you with that. For you as a beginner (I assume?) I would recommend to join a class rather than getting a private tutor. I think it is more fun to learn that way. You can learn through the interaction and!! mistakes in the classroom. The grammar of
Japanese seems pretty doable, but I am just learning it myself. :-)
I would say if you learn Hiragana and Katakana before you come and you take intensive classes when in Japan you will need a year to be fairly fluent. I would check if you can possibly work here as a nurse as in that profession it could be critical one day that you are rather good in the language. In some countries there are fairly strict regulations I think.

But in the end it all boils down to your determination. With that you can overcome any obstacle. You sound very determined, I find that fairly impressive. I wish you good luck!!!

PS. I would really like to know why you are so keen on coming to Japan...

It depends on the individual. The BEST way is to work in a TOTAL japanese environment. (japanese company) where english is NOT the spoken Lang. I learned faster this way. There was NO choice but to speak and understand quickly. The brain usually kicks in the "panic" mode.. this helps..

Good luck

Like the other two said, it really depends on you and how determined you are to learn. It's also best for total immersion, to live in Japan.

If you're taking a one hour class once a week, then forget it. It'll take you forever. If you're willing to spend about 4 hours a day studying (grammar, reading, and vocabulary), then you may be able to reach conversational level in 3 years. Note that this is conversational level. You still won't be able to read a newspaper in Japanese. That takes a whole lot more vocabulary and more time to learn.

You said that you want to be a nurse, which means that you'll have to learn complex medical terms you won't find in the average Japanese textbook. You may also need to learn the more formal Japanese since you'd in essence be serving the public.

The most important words and phrases are all of them. If you are serious I suggest one to thre semesters of grammar study and then a total immersion program. Something where you will have to speak and use Japanese at all times. Given the good basic skill set, you will be able to adapt to all of the specialized terminology. In the medical field, you may have more specialized words to learn.

Do you already have a job waiting for you there ? If not, you just can't go there and expect to be hired. You'll need a work visa. And to get a work visa you need a employer waiting for you! You need to be better than good in Japanese!You'll need to speak as well as a Japanese. You'll also need to read and write Japanese. And that means romaji and kanji ! Not an easy task ! This will take a GREAT deal of effort ! The Japanese just don't hire anyone who wants a job.