OpenCart allows use of multiple languages within a single install. Essentially, they allow multilingual stores.

OpenCart also allows multiple stores running on a single install/instance. It is a multistore software.

So the talk.to OpenCart extension setting page should allow:
1. Mapping of each OpenCart store to a talk.to site
2. Mapping of each installed language for each OpenCart store to a talk.to widget within that OpenCart store.

Store 1
----Choose talk.to site ----
----English
--------Choose widget--------
----German
--------Choose widget--------
----French
--------Choose widget--------
Store 2
----Choose talk.to site ----
----English
--------Choose widget--------
----German
--------Choose widget--------
----French
--------Choose widget--------

In terms of how it should work, that's simple. The javascript code that the extension adds to the frontend of opencart should have if...then...else wrapping the widget code. So before saying which widget should be called, the extension should grab which store the visitor is on, and which language, and call appropriate widget based on that.