Only use Fluent bidi isolation for RTL locales

src/hyperjump-json-schema.test.js

@@ -155,9 +155,9 @@ const isCompatible = (compatibility, versionUnderTest) => {
 
 /** @type (messageId: string, messageParams: MessageParams) => string */
 const getMessage = (function () {
-  const ftl = translations["en-US"];
-  const resource = new FluentResource(ftl);
-  const bundle = new FluentBundle("en-US");
+  const translation = translations["en-US"];
+  const resource = new FluentResource(translation.ftl);
+  const bundle = new FluentBundle("en-US", { useIsolating: translation.direction === "rtl" });
   bundle.addResource(resource);
 
   const disjunction = new Intl.ListFormat("en-US", { type: "disjunction" });

src/localization.js

@@ -24,12 +24,12 @@ export class Localization {
   /** @type (locale: string) => Localization */
   static forLocale(locale) {
     if (!localizationCache.has(locale)) {
-      const ftl = translations[locale];
-      if (!ftl) {
+      const translation = translations[locale];
+      if (!translation) {
         throw Error(`The ${locale} locale is not supported.`);
       }
-      const resource = new FluentResource(ftl);
-      const bundle = new FluentBundle(locale);
+      const resource = new FluentResource(translation.ftl);
+      const bundle = new FluentBundle(locale, { useIsolating: translation.direction === "rtl" });
       bundle.addResource(resource);
       localizationCache.set(locale, new Localization(locale, bundle));
     }

src/localization.test.js

@@ -4,13 +4,19 @@ import { Localization } from "./localization.js";
 
 describe("Localization", () => {
   const fixtureLocale = "fx-TR";
+  const ltrFixtureLocale = "fx-LT";
+  const rtlFixtureLocale = "fx-RT";
 
   beforeAll(() => {
-    translations[fixtureLocale] = `test = unsupported locale`;
+    translations[fixtureLocale] = { ftl: `test = unsupported locale`, direction: "ltr" };
+    translations[ltrFixtureLocale] = { ftl: `type-message = Expected a {$expectedTypes}`, direction: "ltr" };
+    translations[rtlFixtureLocale] = { ftl: `type-message = Expected a {$expectedTypes}`, direction: "rtl" };
   });
 
   afterAll(() => {
     delete translations[fixtureLocale];
+    delete translations[ltrFixtureLocale];
+    delete translations[rtlFixtureLocale];
   });
 
   test("unsupported locale", () => {
@@ -21,4 +27,14 @@ describe("Localization", () => {
     const localization = Localization.forLocale(fixtureLocale);
     expect(() => localization.getBooleanSchemaErrorMessage()).to.throw(Error);
   });
+
+  test("ltr locale doesn't isolate placeables", () => {
+    const localization = Localization.forLocale(ltrFixtureLocale);
+    expect(localization.getTypeErrorMessage(["string"])).to.equal("Expected a string");
+  });
+
+  test("rtl locale isolates placeables", () => {
+    const localization = Localization.forLocale(rtlFixtureLocale);
+    expect(localization.getTypeErrorMessage(["string"])).to.equal("Expected a ⁨string⁩");
+  });
 });

src/translations/index.js

@@ -1,6 +1,13 @@
 import enUS from "./en-US.js";
 
-/** @type Record<string, string> */
+/**
+ * @typedef {{
+ *   ftl: string;
+ *   direction: "ltr" | "rtl";
+ * }} Translation
+ */
+
+/** @type Record<string, Translation> */
 export const translations = {
-  "en-US": enUS
+  "en-US": { ftl: enUS, direction: "ltr" }
 };