This is a point in history that I find interesting. Before I began reading up on it, I too believed that it was an England vs Scotland event. If I understand the situation correctly now, a better description is that it was the House of Stuart trying to wrest the British Crown back from the House of Hanover. Regarding Bonnie Prince Charlie's linguistic abilities (I wish I could remember my source), I read that he spoke Italian, French, English and Polish. No mention of Gaelic though.
As to the French involvement, I get the impression that France viewed the occasion as one more chance to spit in England's soup. I have the same view regarding the American Revolution. I find it hard to believe that the French Monarchy had any great interest in the establishment of a Democratic Republic anywhere in the world.
The actions following the Battle of Culloden were certainly atrocious, but Daz has the right of it when he says that we shouldn't view 18th century events with 21st century standards. The Highland Clans behaved the same way towards each other periodically throughout history. The Acts of Proscription were an assault on Highland culture, but it is my understanding that they were unevenly enforced at best. I believe that the death knell for Highland life came from the "Clearances" a few years later.