String encapsulation for improved translation

I don't know why, but I seem to like the look of `$1` better than that of `%1`. Not that I can think of any objective reasons to prefer one over the other. Also consider e.g. `{1}` or `[1]`.

> I think that the "wide char" problem might be relevant for % syntax too, however.

Unlike with some of the others I can't spot any visual difference, but indeed [it exists](http://www.fileformat.info/info/unicode/block/halfwidth_and_fullwidth_forms/list.htm) (as clearly does full-width just about anything you might reasonably want to use).

> The charm of the % variant, as I see it, is that it does not leave translators with the feeling that there is something to translate about variable names / placeholders.

On the other hand, if you mess up what `$1`, `$2` and `$3` mean the problem might not be immediately apparent. You could never accidentally type `"currently displaying page {total_pages} of {current_page}"`.