filter: Use Intl.ListFormat rather than .join(", ").

web/src/filter.ts

@@ -976,11 +976,7 @@ export class Filter {
                 }
                 return person.full_name;
             });
-
+            return util.format_array_as_list(names, "long", "conjunction");
-            // We use join to handle the addition of a comma and space after every name
-            // and also to ensure that we return a string and not an array so that we
-            // can have the same return type as other cases.
-            return names.join(", ");
         }
         if (term_types.length === 1 && _.isEqual(term_types, ["sender"])) {
             const email = this.operands("sender")[0];

web/tests/filter.test.js

@@ -1495,7 +1495,11 @@ test("navbar_helpers", () => {
 
     // make sure title has names separated with correct delimiters
     function properly_separated_names(names) {
-        return names.join(", ");
+        const names_internationalized = new Intl.ListFormat("en", {
+            style: "long",
+            type: "conjunction",
+        }).format(names);
+        return names_internationalized;
     }
 
     function test_redirect_url_with_search(test_case) {
@@ -1709,7 +1713,7 @@ test("navbar_helpers", () => {
             terms: dm_group_including_guest,
             is_common_narrow: true,
             icon: "envelope",
-            title: "translated: alice (guest), joe",
+            title: "translated: alice (guest) and joe",
             redirect_url_with_search: "/#narrow/dm/" + joe.user_id + "," + alice.user_id + "-group",
         },
         {