If Firefox is consuming 45% of CPU time while just sitting open, there is a problem. Languages, I don't know how that works. My gut feel is it shouldn't have a big impact. I installed language support in Win xp on a 1 Gb ram Pentium D rig- not much difference. Actually, your Firefox mem use of 12% with 2 Gb installed seems proportional to mine with less than 3% with 8 Gb installed.
I don't know. Hardware is hardware. It's all capable of so many operations per second. And when it doesn't it is the software that hinders it.
i5 3570k, ASRock z77 Extreme 4, 8 Gb Ripjaws 1600, Antec 430w psu, HVR 1600 tv tuner, custom case- marble top, oak face. Carver & DCM Time Window sound system. Mint 14 KDE.