Change post url depending on language

I have a Web page that has a blog. It has a static home page, and you can access the menu using the top menu.

When I visit the main blog, it looks like:

www.mysite.com/blog

When I go to the translated blog (in this case, the English version) it looks like:

www.mysite.com/blog-2

I want it to look like:

www.mysite.com/blog/en/

I used permalinks like this:

/blog/%postname%/

I tried:

/blog/%lang%/%postname%/
With no luck…

How can I make it sensitive to languages?

EDIT: Plugins I’m using:

• Polylang
• Lingotek