Change language for one application (Google Now voice recognition, root available)
There is a way of forcing a certain app to be in different locale / language than your general phone settings!


you need to be rooted
install "xposed framework" from xposed.info
within this app install a module "app settings"
within this module search for "quicksearchbox" (it's the google search app)
change its locale to "english-us"
enjoy


Unfortunately xposed framework stopped working with android 5.0 Lollipop... so enjoy it until your phone is hit with the update :(