Change node language from Language neutral to English in bulk using VBO
Oh, yes, I remember this pitfall. Here's what happens: assuming the default language of your site is English, any Language Neutral node is assumed to be English. If you look at the node table in the database, you'll see that their language is 'und'. This is per content type, so let's say we have Language Neutral Basic pages. If you now add a Basic page with language English, its body won't be displayed, though if you check the database, you'll see that it's there (and the node's language is 'en').

The moral: all English-language nodes of the same content type must have language set to either 'und" or 'en', or the ones set to 'en' won't display. On our site, we set the critical content types to Require language (Don't allow Language Neutral). (Under Admin -> Structure -> Content types -> Edit -> Multilingual settings.)