3. Tech News, Blogs(incl blog/article publishing platforms, like Hatena Blog, Qiita)
This is one of the most used/referred media for JP developers, I think.
If I have a programming question and try to Google it(in Japanese), I get most of the top results from those sites in this area, meaning that not from Q&A sites, but Qiita, Hatena Blogs, and professional tech news articles.
When I do the same in English, I get SO pages at the top of Google result page.
It is worth to mention, that Qiita is one of the programmer’s best information source in JP, and most of Google’d tech/programming questions can be answered by it, but they have some problems too.
The problem is that there are so many novice level, poor quality articles in Qiita, and it makes people to have hard time to get right answer to their question from Google’d resulting Qiita pages.
I personally get rid of Japanese answer from Google result, not to waste time for this reason.
It is okay, since most of authors are amateur/non-professional article writers meaning that they do not earn money from writing it, but it is a problem for some people anyway.
I guess it is by their(Qiita’s) intention to allow(not to down vote/credit) novice writers write novice articles. By doing so, by letting people feel easier and willing to write articles, (and not get down votes) , they have more articles in their site, and in the end it will help users/reader developers to get answers to their question from inside Qiita.
Stack Overflow, on the other hand, they have a credit system, which makes users to down vote to poor quality questions and answers, so poor content get less chance to be read, that is not the case with Qiita, they only have up-vote(+1).
As you might already be familiar with it, Japanese culture and Japanese people are considered to be modest, and not liking speak bad of someone, and even someone’s opinion even they think the opinion is wrong or poor.
From this cultural reason, people tend to avoid down grade(-1) to other’s opinion/articles/answers.
Aside from this article(Google’d result) quality issue, yes Japanese developers can get good amount of information from those sites, without reading English pages.
4. General purpose communication sites incl SNS (Facebook, twitter, etc)
This highly depends on the connections/friends of one’s, but many questions are asked and answers in Japanese, meaning that this is one of good sources of information for many developers too.
To summarize, It can be said that Japanese developers can get good amount of information only from Japanese sources.
But also, those expert level developers may sometimes have hard time getting right answers from Japanese sources, and go for English ones.
This is one of the reasons, some people say “expert level developers are, to some degree, able to read English”.
So, in my opinion, it is not much important for (esp novice level) developers to have skill to read english, compared to those developers in other countries, because we have so many good Japanese information sources.
When the one gets more experiences and reach to higher levels, they tend to feel the needs of English reading/writing skills.
But they can live without it, anyway.
If they really feel the need of referring to English source, they can use translation tools.
This is an off-topic answers to your question, but something I’d like to add.
I spend some of my weekend time(as a volunteer) for teaching computer programming to elementary to high school students.
Since most of the programming languages are English based, so for those learners have hard time reading/writing a code in English.
This is true especially when a learner’s age is low, like 6-8(or even lower), since they may not have learned alphabet characters, yet.
Even if they know alphabet characters, they may not know the meaning and pronouciation of words, like “function, if, while, each, case” etc, which makes it harder for them to learn programming.
For this reason, it is the hardest to learn real programming languages(C, Java, Python, etc) for kids/students, then Visual (GUI based but labeled in English )programming languages (like Scratch), then Visual with no label programming languages(like Scratch Jr)
There are some Japanese based programming languages, but they are not so popular, yet.
Actually, I have a feeling that it is fun learning programming for most of kids, they manage to handle this English problem, anyway, and concur.
This is the power of “fun of learning programming” 🙂