Google Maps WebService language is always English

I'm using Google Maps Web Service for my new app. In Google documents mentioned that for changing the language of API I have to use language parameter. For example in Directions API I use this URL to get results of directions :

http://maps.google.com/maps/api/directions/json?origin=lat,lng&destination=lat,lng&units=metric&mode=walking&lang=fa&region=ir

or

http://maps.google.com/maps/api/directions/json?origin=lat,lng&destination=lat,lng&units=metric&mode=walking&lang=fa-ir

But no difference API always return me html_instructions in English like this :

"Turn \u003cb\u003eright\u003c/b\u003e toward \u003cb\u003eKolahdouz Blvd\u003c/b\u003e" Turn right toward Kolahdouz Blvd

I test Google Maps official app on an Android device when I get directions between two points when my phone language is set to Persian it returns me strings in Persian. enter image description here How to ask Google API to return me localized strings?

Thank you