I worked in Japan as a dev for a few years. I was already quite fluent in Japanese. I’d recommend finding a job with a foreign org first, where many people already speak English. Most Japanese companies won’t have much experience around visas (you can do it yourself, a bit annoying). No one is hiring you for language skills, they are hiring you for your software skills. Get your foot in on the door, get a visa, then figure it out.

Don’t feel like you need Japanese to get a job. Getting to a point where you can fluently discuss software engineering with our devs will take many years - don’t let this be a blocker, just find a job where you can use English so you can be there, see if you actually like living there, and figure out the rest as you go.