Hi, I'm new to silverstripe I have some issues and I would like to understand the best ways to solve them.

1) I have a multi-site installation that is 5 sites which are different but, from time to time (even often) could "share" some pages (having a copy of the page could be a solution as sometimes the pages on the different sites are just "similar" not "identical". What is the best solution?

2) Any single site must be presented in 3 languages, the pages in the different languages are "identical" (except for the translation). Copying a page doesn't seems to me a perfect solution if after this I have to maintain different pages (if I change the layout of a page I want to change it only once). What is the best solution?

3) If I add some "block"/"widget" of "my" code that will call one of my backend API, what is the best way to translate the strings that comes back from the API? Do I have to provide a translation system on my backend or is there a way to this in concrete?

Thanks,
Cosimo.

1&2) Look at either Translatable or Fluent
You may also be interested in something like: http://addons.silverstripe.org/add-ons/martimiz/silverstripe-languageprefix (for translatable iirc)

3) You will need to provide either translations, or a translation service to pass it through.