This is a good example of when to use tags vs categories. There's nothing wrong with having varied content on a blog, or any other kind of web site. You just want to:
- Ensure people can get to the content that they want, and only what they want via various readers
- Pay attention to the topics that interest people the most and make sure that those people get something new to read fairly frequently
Try to resist the urge to create more than ten categories. Five would be better. Beyond categories, make good use of tags to organize your posts.
Lets say that you have five main interests:
- Unicorn breeding
A list of categories on your blog will then direct people to the topic that might interest them. Lets pick unicorn breeding (a favorite of mine) and say that I read a really good 'rant' that you wrote regarding forged pedigrees. If you tagged that post as a rant, lets say with 'rants', I might also discover that I most enjoy your writing when you are adamant and annoyed.
This lets me pull two feeds:
- One from your 'Unicorn breeding' category
- One from your 'rants' tag that will likely put content in front of me that I would not have seen otherwise.
I strongly discourage posting in several languages, unless you are using some sort of plug-in or facility for translations which should allow people to subscribe only to posts available in a certain language. Google recently added new sources to their news mash up, lots of people are complaining that they are now getting French articles in their reader, even though their preferences are set for English.
Mixed and varied content for a personal site is not a bad thing, its just going to increase ways for people to find you, which hopefully results in quality organic inbound links. Its also nice to know that people actually read and appreciate what you have to say.
If you were running something like 'Pro Technology Blog', where the title and topic of the site suggested that the content within would be equally specific, it would be a bad idea.
Just use tags strategically and make sure you pay attention to what gets the most attention. The point is to get long term readers who actively participate in discussions and help promote your blog.