Yes and no.
I have developed my personal blog in Romanian and it's a 'mix-topic' blog. I do tend to write more about freelancing, saving money and travels for instance, since I have more experience in the topics.
When it comes to the international blogs though it's better to have a clear niche. I don't advertise my Romanian blog, since I get enough traffic from commenting on other blogs and Google. For an English blog though it's better to be more 'niched', you can build your SEO better and also attract the exact type of readers you need.
Am not saying you cannot win with a general blog, but it's safer to choose a niche.