Because there is not a linguistic census in France, as there is for Britain, there is difficulty in estimating

Because there is no linguistic census in France, unlike Britain, it is difficult to estimate

Unlike Britain, there is no linguistic census in France, and that fact makes for difficulty in estimating

There is not a linguistic census in France, as there is for Britain, a fact making for difficulty in the estimation of

There is no linguistic census in France, as there is in Britain, a fact that makes it difficult to estimate