Yes, you can. English is just part of communication. You should have strong programming skills. Not only to work in Silicon Valley but anywhere else outside Japan(In Japan Japanese is more than enough). However you will get some communication gap in the beginning, but as I know Japanese people can write good Japanese only the issue is the conversation(Do reconfirm your task by writing on board during discussion). Once you are in outside Japan, English is a necessity and I am more than sure if there is a will there is the way. I am living in Japan for last few years and in the beginning, I was on 0 Level Japanese and now N3 Level. It's just the way how you have interest in new language. In employer point of view if you are a super engineer (Very good programmer) you will be an asset to them not now but a year later.
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