Define rules in the settings to load the theme you want according to 3 parameters :
- the current site
- the current language
- the current url path, this can also be a regular expression if enclosed in slashes. example
/for the homepage.
The first rule that match will define which theme will be used. Organise your rules to have the most specific first.
If no rules match, the default theme will be used.
For non web requests, the default theme will be set.