One of the most FAQs in these programming forums is which language to use for your application. I found a great blog post on this, and wanted to share some points with those who are asking similar questions. Some summarized points from the article One person mentioned something else I felt was important: don't settle for what you know, if you want to know something else. Do that project in Python if you really want to learn it. For those who are thinking of choosing something else because their language of choice gets bashed constantly: "There are two types of languages, those people complain about, and those that nobody uses." - Bjarne Stroustrup Link to full blog post
Great post friend. But I would like to add something: If your project is a medium-large project then it is best to plan for the future. So, languages that are more modular, less prone to errors, more portable are better to use, even if it cost you some time in the beginning to learn.
I'm with the author of the blog post on this one. All languages accomplish the same thing, and scaling isn't something you ever need to worry about when first developing a project. Hardware is so cheap these days, if something gets successful, you could just scale vertically until you hit the limits. Plus, it's an easy task to set up memcached and several slave database servers. With VPS hosting, it's a few clicks to get a new server or servers going.