I wish to turn this blog:
Into a feed, through a tool like yahoo pipes or something else.
That site already has a feed, but it can't produce a feed only for the English category posts.
It looks as though the site is using tags for its various languages and not categories. You can get a feed of all the posts tagged in English at the following:
However, some posts are tagged both English and French, so you could do something through Yahoo pipes where the feed contains the tag English and not French.
Another approach might be to pipe the feed through the translator so that any posts in French would get translated to English, as outlined here.