My take on this:
PHP - IMHO not worth much today, although I sometimes grab it when I need some website scripting that doesn't run on my own machine
Python - I pick this if I can. And it's a great productivity tool. But not essential to do the job.
Javascript/jQuery - All aboard the hype train. It's probably subpar to PHP for me.
Assembly - Not very practical. These days only very useful if you want to squeeze the upmost cycle of an algorithm for power efficiency and/or throughput. But remember that productivity in this language low, and probably not a very good initial starting point.
C - This is my vote. Most widely used for embedded micro's in electronics. I would have combined this in-line assembly in C. Because sometimes you can't avoid it. I also want to emphasize that with C, although you don't write assembly, you should read the assembly code sometimes the compiler generates.
C++ - would be my 2nd choice to C, can be used for some embedded platforms, and also to build Qt applications and various other bits and pieces.
Additionally, after having briefly looked at your website, please don't mix up Arduino and C. Arduino themselves don't want to admit you program C or C++, but rather their processing language or whatever. Under the hood you lay out a C-style program (often) but refer to C++ objects and libraries. Headers/prototypes/references to other .ino files are automatically generated, which is all very confusing.