Add localization hint for payment sheet

* Adds "lang" member to PaymentRequestInit dictionary
* Adds processing model for `lang`
* Optionally allows UA to localize the payment sheet

closes #650

Author: marcoscaceres

index.html

@@ -751,8 +751,24 @@ 
               li>
             ol>
           li>
+          <li>Let <var>uiLangvar> be null.
+          li>
+          <li data-link-for="PaymentDetailsInit">If
+          <var>detailsvar>["<a>langa>"] is present:
+            <ol>
+              <li>If <a data-cite=
+              "ecma-402#sec-isstructurallyvalidlanguagetag">IsStructurallyValidLanguageTaga>(<var>detailsvar>["<a>langa>"])
+              is false, throw a <a>RangeErrora>.
+              li>
+              <li>Set <var>uiLangvar> to <a data-cite=
+              "ecma-402#sec-canonicalizelanguagetag">CanonicalizeLanguageTaga>(<var>detailsvar>["<a>langa>"]).
+              li>
+            ol>
+          li>
           <li>Let <var>requestvar> be a new <a>PaymentRequesta>.
           li>
+          <li>Set <var>requestvar>.<a>[[\uiLang]]a> to <var>uiLangvar>.
+          li>
           <li>Set <var>requestvar>.<a>[[\options]]a> to <var>optionsvar>.
           li>
           <li>Set <var>requestvar>.<a>[[\state]]a> to "<a>createda>".
@@ -935,8 +951,11 @@ 
           <li>
             <p>
               Otherwise, present a user interface to allow the user to interact
-              with the <var>handlersvar>. The user agent SHOULD prioritize
-              the preference of the user when presenting payment methods.
+              with the <var>handlersvar>. Optionally, if
+              <var>requestvar>.<a>[[\uiLang]]a> is not null, localize the
+              user interface to match, as closely as possible, the language of
+              <a>[[\uiLang]]a>. The user agent SHOULD prioritize the
+              preference of the user when presenting payment methods.
             p>
             <p>
               For the <a>payment handlera> selected by the end-user, the user
@@ -1286,6 +1305,15 @@ 
               accepts the payment request.
             td>
           tr>
+          <tr>
+            <td>
+              <dfn>[[\uiLang]]dfn>
+            td>
+            <td>
+              The merchant-preferred language in which to localize the UI when
+              <a>show()a> is called.
+            td>
+          tr>
         table>
       section>
     section>
@@ -1575,6 +1603,7 @@ 
           dictionary PaymentDetailsInit : PaymentDetailsBase {
             DOMString id;
             required PaymentItem total;
+            DOMString lang;
           };
         pre>
         <aside class="note">
@@ -1586,7 +1615,17 @@ 
           <a>PaymentDetailsBasea> dictionary, the following members are part
           of the <a>PaymentDetailsInita> dictionary:
         p>
-        <dl>
+        <dl data-sort="">
+          <dt>
+            <dfn>langdfn> member
+          dt>
+          <dd>
+            A [[!BCP47]] language tag representing the preferred language of
+            the financial transaction. The <a>langa> member serves as a hint
+            to the user agent, optionally allowing the user agent to localize
+            the payment UI to be in the same language as the document that made
+            the request for payment.
+          dd>
           <dt>
             <dfn>iddfn> member
           dt>