As a former military man who has worked with the French (and enjoyed the experience):
The last war with the French was nearly two hundred years ago. We have had almost continuous treaties and co-operation since then (Crimean War onwards). Britannia can't afford to rule anything on our own and have not been able to for some time. Pooling some resources and sharing technology does not in any way mean we cannot act alone if we want to (though another Falklands type action has been beyond our capability for many years already). Sierra Leone type intervention will continue to be within our capabilities. It does however mean we can save some money that can be used elsewhere for other (possibly) more important military capabilities.
As regards language - previously English has been used as the "operational language" (just like in aviation) - so lucky us, although there is no reason why we can't learn some French.
The French are our most logical choice of ally (and likely a more equal relationship than with the U.S.) Our military has been hollowed out (like a rotten log) for many decades now - tough decisions needed to be made, instead of burying our heads in the sand whilst waving our flag patriotically.