My blog is a bit biased as I’m most active in the Ruby community, so that’s where I see the most opportunities. Overall, I would say there are more companies that are looking for PHP developers than companies looking for Ruby developers, but at the same time there are more PHP developers than Ruby developers, so I think there is more competition for the jobs as well.
While some companies are looking for people with experience in a specific language or technology, more importantly they are looking for good developers. New languages can be learned pretty quickly - when I started my first job, I didn’t have any experience using Ruby but was able to pick it up in a couple of days.
I wouldn’t spend time learning a specific language in the hopes of getting a job with it. The popular languages and technologies are constantly changing, so if you need to study one before getting a job with it, you’ll always be behind. Instead, I’d focus on things that make you more employable from a long term perspective.
One of the most important things you can do to make yourself more employable is have something that demonstrates your talents as a developer. This could be an active blog discussing development related stuff, contributions to an open source library, your own web service, or something similar. Having something like that puts you ahead of 95% of developers out there, so if I was to invest in anything to make myself more employable it would be that.
As for your chances of getting a job here, as I outlined in this reply, until you actually come to Japan, there’s no way to know if you’ll be able to get a job or not.