I'm generating PDF files using Apache FOP 2.1. 

For this I am trying to set the default language to be English.  

This is supposed to be verified after the creation of the PDF via Adobe Reader's option File/Properties/Advanced/Reading Options. This value currently is empty. 

[![Image showing language is not set](https://i.stack.imgur.com/7ft7T.png)](https://i.stack.imgur.com/7ft7T.png)

I have tried setting `xml:lang="en"` in `fo:root` element, in first page-sequence or in the very first element of the `.xsl` file... Nothing seams to do the trick. 

Any Advice?  

 Thanks Dimitris. 

**Update:**  

I have tried 2 more options as suggested in the answers, neither of the 2 worked 

1. `<fo:declarations>
<pdf:catalog xmlns:pdf="http://xmlgraphics.apache.org/fop/‌extensions/pdf">
<pdf:string key="Lang">en</pdf:string>
</pdf:catalog>`
2. `<x:xmpmeta xmlns:x="adobe:ns:meta/">
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#">
<rdf:Description rdf:about="" xmlns:dc="http://purl.org/dc/elements/1.1/">
<dc:title>the document title</dc:title>
<dc:language>en</dc:language>`

***Update 2***  

Have started a bounty on this question.  

Any help appreciated and rewarderd