"We are seeing huge demand from our members for core Linux developers, especially in the embedded market. This is one reason we created a series of training courses to help educate the next generation of developers. Also, if you can demonstrate your knowledge of open source development with examples of code you've written and submitted, you will impress potential employers. Code is your resumé in this business.
What languages? It depends on your field of interest. Someone always asks "Which language is the best" and the answer is always "It depends." You won't know until you define what technologies you are interested in, and try some different languages to find out which ones fit. A programming language is like any tool: some feel right, some don't.
The three big fields of growth are embedded, mobile, and cloud, with lots of overlap between them as we moved to a fully-networked world. (The wholesale stripping away of our privacy, and data-mining us all for fun and profit, must be countered, so might I suggest baking in user protections as part of your fundamental functionality?)
Other desirable skills
The field is wide-open for people who aren't into coding, but still want to find opportunities in FOSS. This networked world places new demands on system and network administrators. Energy management, cloud technologies, databases, high-availability, provisioning, monitoring, and security require new and advanced skills. Artists, musicians, tech writers, community managers, hardware designers, reverse-engineers, translators, publishers...if you look, you will find a niche you like. As McPherson said:
"But it's more than just code for the best opportunities in this market. In the future, to really write your ticket you should show you can lead a project, write persuasively and work well with a large, distributed community. People who thrive in less structured roles will have great success, whether in development, sales and marketing or anything else. Those who can come up with their own job descriptions and do what needs to be done will be best suited for these types of roles."
McPherson hits on a key point, and that is being self-motivated. That is the key to success in any field, and especially in FOSS.
Holger Dyroff, VP of Business Development at SUSE, also recognizes the importance of diverse skill sets: