In an ideal world:
In an excellent article Don't Call Yourself A Programmer, And Other Career Advice, Patrick McKenzie explains, among other things, that language doesn't matter:
A developer is a person who solves problems, in general. A developer is not a person who writes code in a specific language.
Businesses don't care about the languages you know. If they need to hire a developer for a project written in a specific language, and they have a candidate who is highly experienced but never wrote a line of code in this language, he would still be hired.
According to my experience both as a developer and as a person who had to hire other developers, the observation is very similar:
The N years experience in Java or N years experience in C# doesn't matter. What matters is that the candidate knows how to solve problems, knows the difference between spaghetti code and clean code with well-thought architecture, etc.
I don't care about the languages you used before. For a C# project, I'll rather hire a professional developer who spent his life writing Java, Python and Ruby on Rails code rather than a beginner who knows only C#, and knows it badly.
The knowledge and the experience you gain using one language is mostly reusable in any other language.
An experienced developer who used Ruby on Rails for web development and spent the rest of his career writing Java desktop applications using Oracle fits perfectly well for an ASP.NET MVC project using Microsoft SQL Server. Because this person already knows everything she need for this job, aside a few specific things and syntax differences.
On the other hand, a person who have done just a few ASP.NET MVC small websites doesn't fit at all, because she may not completely understand the MVC architecture, may know know what is SQL profiling, and may lack some other essential knowledge.
Don't tell me that I'm unable to fix a small problem with a PHP website which uses CodeIgniter just because I never used CodeIgniter before.
In practice, when I search for freelance jobs and when I see the job offerings in general, they are very language-specific.
Some would search for a PHP developer with two years experience in Magento. Others will be searching for a person with VB.NET experience of at least three years, and if you send them a resumé mentioning that you've done C# development for six years, but with no mention of VB.NET, they will not bother to answer. If they ask for a person with an experience with Firebird, they will not listen about your ten years experience with Oracle.
Why there is such difference between the theory and what Patrick McKenzie and I describe as being common sense, and the real world of job offerings?