It is not necessary to go through official classes to learn Japanese. It is a simple as purchasing a Japanese language book that best suits ones learning preference as it mostly self-discipline knowing we want to learn.
While browsing through various study books and you find one that flows with the way you wish to study, then just purchase it! Refrain from keeping too many books that you will not have the time to read and focus on.
Underline and highlight the words you have difficulty understanding.
Seek out and ask friends who are good at Japanese.
Practice your writing and listening exercises.
Kanji characters need more time and more individual effort than writing and speaking. When learning Kanji, buy proper Kanji textbooks to help with memorizing the characters. Learn and practice them more to remember.
The Japanese Language Proficiency Test is held twice a year. You can check their website to find out when and where you can take the test. If you can pass the tests to obtain at least an N2 level in Japanese, you can proceed to apply for a job in Japan.
Additionally, with special skills like a car mechanic graduate specializing in piston, all you need is a certificate to apply directly to a relevant job via the internet and go through Skype interviews (in Japanese). These options are all free and you will not have to spend a lot of money.
Of course, you can pay an exorbitant amount of money to bypass the actual time and effort, but this is a risk. You can lose these amounts of money and have your hopes dashed when it does not go through successfully. What we need to understand is that there is nothing instant in this world. Try to take the JLPT certificate offered by The Japan Foundation and avoid private independent Japanese language tests.
Remember, the JLPT tests are of high quality and as the Japanese government agencies are strict in monitoring the standard of the tests, it is easily recognized globally.