I am currently maintaining a multilangual website with one, identical design that handles about 10 different languages. Each website is being managed by a dedicated team from a specific country - they add their own, unique content, they also want their own, unique fixes/improvements etc. so it's not possible to make one, universal template and add/edit/delete content only - all layouts are partially customised for specific teams.
Right not each variant has it's own copy of the whole template with all the files. It's completely inefficient since even small modifications that must be added to each language takes forever to implement and spread along all the websites' versions.
Using sub-themes that inherits all the files from basic theme looks like a good idea to solve most of my current issues. I've read about it, played with it for a while, checked how does inheritance works and tested it. I've also downloaded Zen, just as I always do since it's a great starter theme - but I started to wonder if it really should be used in my situation. Even Zen's guide says not to modify any file from basic theme.
I've got a question for any developer with experience in theming.
Is it better to use a starter theme like Zen and greatly modify it when creating basic themes to use inheritance functionality or to start with a blank project and create everything from scratch? What is more efficient and yields more future benefits?