I hear from people that people not from japan usually have a very low chance of becoming a successful mangaka, why is this? I already know that it's because they don't know japanese, but what else?
Deeply ingrained xenophobia.
I think there's a lot of communication involved in this job (for instance with the editors), and lack of japanese language skills and cultural references is a problem,...
Furthermore, if the mngaka can't write in japanese, someone will have to translate and edit the typography, raising costs, slowing production.
This creates large disadvantages for the mangaka in a very competitive market. So no need to accuse people of racism, without further evidence. In reality the mangaka should start his/her carreer in a country with a language he can speak.
You could always write something for Tokyopop. It seems they're willing to publish any sort of crap.
There are wonderful manga-influenced works by Americans and other Non-Japanese, you could call it manga even. (the newer somber works of Dan Kim, MBQ, Kabuki) But then there's the cheap "profit over the popularity of the term" stuff.
A Kodansha's manga editor said he met some overseas mangaka-wannabe and read their works, but none of them were better than countless Japanese mangaka candidates. Some of them can draw estimable artistic drawing, but they all are lacking the basic sense and technique of manga, like the use of panel layout and focus line. Most notable is the horrible layout of speech balloons. He always give then advice to consider balloons as parts of your artwork. A tasteless oval balloon is beside the question.
For your interest, one of those techniques is that, when a hero and a bad guy fight, the hero should be in left side of the panel and the bad guy should be in right side of the panel. This theory is true in anime too. Check AKIRA manga and anime if you can.
"I already know that it's because they don't know japanese, but what else?"
isn't that really reason enough?
>>5 Hey could you get me that interview? I'd be really interested in reading it.
The guy who wrote MBQ, Felipe Smith, is going to get a new story serialized in Kodansha's Morning 2
So I guess it is possible to become a "lol mangaka" in Japan.
http://www.animenewsnetwork.com/news/2008-04-28/kodansha-morning-2-to-serialize-felipe-smith-comic
I'm pretty sure >>5 is on to it here. Most westerners who want to be mangaka really don't understand the medium well enough to make something that fits in.
You have two choices: Go with the mainstream, which I imagine most would try, but here the competition is fierce, and any lack of understanding of the basics of the medium really hurt you. The other option is to go for the off-beat, alternative publications. This is where a non-Japanese would have a far better chance to succeed, but of course, success there doesn't get you very far anyway.