Since that things changed for the good in Tiki.
That’s great you are willing to improve and help us to make Tiki better.
- Identify, check language Tiki use at : https://sourceforge.net/p/tikiwiki/code/HEAD/tree/branches/18.x/lang/
- Improve layout : Actually most of it work comes out from bootstrap from time to time we found that a change of class under rtl direction work better so this is the kind of things you can commit or report to http://dev.tiki.org
I don’t think we really do (or want) CSS custom anymore it should be handled using Bootstrap. (of course they may be exception)
Not sure what "using Bootstrap" mean talking about upgrade.
Please report bugs or issues to http://dev.tiki.org hopefully someone will have a look.
Have a nice day,