Interesting. I was going by this list:
http://en.wikipedia.org/wiki/Notepad...ming_languages

Which doesn't list BASH as a supported language. Are there others not shown there as well?

Bash is part of the family of shell scripts. Shell scripts are supported.

And about IDL, or any other language, anyone could always create a custom highlighting for those:
http://sourceforge.net/apps/mediawik...Language_Files
http://stackoverflow.com/questions/1...x-highlighting
http://pocaracas.wordpress.com/2009/...ng-in-notepad/

And for autocompletion as well, someone could contribute an XML file for that (to be placed in "plugins\APIs"), but a custom file could always be easily made for it if there's none.

Maybe sometime I'll try to improve bash support in Notepad++ by creating my own user files (including the one for autocompletion). I'll share it here if I still remember

Extracting a list from a latest styles file, it shows that these are the supported languages/syntax-set by default: ActionScript, ADA, asp, Assembly, autoIt, bash, Batch, C, C++, C#, Caml, CMakeFile, CSS, COBOL, D, DIFF, GUI4CLI, Dos Style, Fortran, Haskell, HTML, ini file, InnoSetup, Java, Javascript, KiXtart, LISP, Lua, Makefile, Matlab, NSIS, Objective-C, Pascal, Perl, php, Postscript, PowerShell, Properties file, Python, R, RC, Ruby, Scheme, Smalltalk, SQL, TCL, TeX, VB / VBS, Verilog, VHDL, XML, YAML

Turns out that shell script support is actually about bash. (In menu it's accessible as L->S->Shell, but looks like it's likely basing keywords from bash).