Javascript and JSON will not allow you to safe the content anywhere. Javascript is great to bring client-side interaction to a webpage. JSON is great for transporting data from A to B. Neither are equipped or particularly well suited to persistently store content anywhere.
PHP is one viable option, but certainly not the only one. There are a lot of other languages out there that are capable to do the same, such as Ruby, Python, or Perl just to name a few. Depending on the platform that your server is running on, ASP.NET might be an option as well. This is all but a limiting list, though. I wouldn't say that the possibilities are endless, but for all intents and purposes they might as well be.
Databases seem like a good candidate, but again, not the only candidate. I've seen blogging systems that use plain text files on the host's file system as their storage "system" - minimalist, elegant, and very flexible.
Then again, you could ask yourself whether you should really try to roll your own blogging system - plenty already exist, most of them freely availabe and more often than not with sundry of themes to pick from, which you could alter to your needs or just use as inspirition/guidance to make your own theme.