Language file working regardless of the theme – as far as I know the answer is no. Also check here.
If you do not want to edit XML files, you can still change colors by selecting Define your language...
item in menu Language
and change the colors of syntax categories using color pickers.
Adding your language into list of built-in languages is not easily possible unless you wish to play with N++ sources. You are supposed to use user-defined languages for standard tasks. However you can:
disable all unnecessarly languages in
Language menu
section inPreferences
window and uncheck theMake language menu compact
so you will get flat list of languages in menu.access your language menu item faster by pressing Alt+L, then 2×Up and Enter