Collections are not dynamic, so the won't populate based on keywords or other metadata.
You could build collections for English and French and put corresponding articles into each. Then readers could choose to look into their preferred collection, or you could sell/restrict access to one or the other.
A note on keywords -- eventually these may be available to users, their potential use in building a dynamic collection or in search are possible uses sometime in the future. Whereas internal keywords will not be visible to the user, so these are better used inside of DPS 2015 by you.
Both types of keywords are good candidates for use in mapping rules -- this controls which card design displays the card. So an article with an internal keyword of "English" might get one card design, and "French" results in a different card design. That would provide visual identity to content with those keywords or internal keywords.
HTH -- Colin