Why is the replacement not happening when using the Search and Replace Scanner module?
Your scenario sounds similar to what is described in issue # 2616640. 

Have a look at Comment nr 6 in it for an explanation for what may be causing it, i.e.: 


  It looks like the module assumes that the field content to replace is set to the same language as the node.


Probably your best bet is to try the patch attached to Comment nr 18.