that way you can use what you're familiar with but talk to tons of brokers and data feeds, and be able to have fast backtesting without reinventing the wheel.
I would mirror what tradelink said, but on the Java side. There's JRuby, which is a Ruby interpreter running atop Java. This means that you can interface with any library accessible to the JVM from your Ruby code.
IIRC, Marketcetera makes use of this to let you define trading strategies in Ruby. Could be useful.