translation adding to website

I already have a cms site build but out client requests the site to be in various languages. At the minute we are just concentrating on two languages. We already have had the site translated professionally so we just need to slot it in when the language options have been created in the database. The language options must have options withing the admin area of cms to change between the two for easy editing. On the main site there will be flags so the user can select which language they prefer. Also as addition to this, i require the language to have a defaul defending on which browser they use for example if someone in france tries to access the site there automatic defaul will be the french version as opposed to someone in the uk version.