Explain field's language opposed to node language
If you use the module Entity translation you have the possibility to say that the body field can be translated but the image field should not be able to be translated.

In your example this would mean 

The value of $node-&gt;field_body will have different values for the different languages the field is translated to. I.e $node-&gt;field_body['en'][0]['value'] could differ from $node-&gt;field_body['sv'][0]['value'].

But at the same time the image field will only have value in LANGUAGE_NONE.

Before the most used setup to have a multilingual site was to use the  Internationalization module, which would create a new node when a translation of a node was done. The new approach with entity translation translates the fields instead. 

Worth noticing, the Internationalization module can be used together with Entity translation. I am only stating the older solution to multilingual sites.