keep ui_locales param in custom policy sign in flow

Hi, 

I'm having some trouble with the language customization of our AD B2C based authentication pages. In my country (Greece) even though the local language is greek, it's very common to use english as the default language for web tools and specifically browsers.

In our business we do want to show english translations but only when user needs it. There is a language switch added in a custom html template that changes the ui_locals param and refreshes the page. We have added LocalizedStrings to our custom policies and initially force the ui_locals=el param in order to override the default browser language and set it to greek. This works fine in the first screen where users are asked to add their email address but as long as they proceed to the next step, the ui_locals param is lost and the password screen is shown with strings in english. 

Is there a way to tell to a custom policy to respect the ui_locals param when moving from one screen to another?