Handling WebMail cache
If you make any modifications in the product, be it language file updates or source code tweaks, you will need to make sure your browser gets the up-to-date content. And while pressing Ctrl-R / Ctrl-F5 or using built-in browser tools for purging cache might work, sometimes it's not enough.
When rendering the interface and working with cache, WebMail Lite relies on current version number, and if it wasn't changed since the previous request, cached content will be delivered. You can force refreshing cache by updating version number, it's stored in VERSION file found in root WebMail Lite directory. It wouldn't really matter which number is specified, it just need to be different from the previous one.
Note that aside from browser cache, WebMail Lite maintains its own cache under data/cache directory. That cache is used for building translated texts as well as templates, so you can try purging content of that directory if you're having problems with not getting visual updates.