feat(i18n): per-app language in system settings; missing translations warn

app/build.gradle.kts

@@ -39,6 +39,12 @@ android {
         testInstrumentationRunner = "androidx.test.runner.AndroidJUnitRunner"
     }
 
+    androidResources {
+        // Lists the translated locales in the manifest, so Android 13+ offers a per-app language
+        // in system settings. The default locale is named in res/resources.properties.
+        generateLocaleConfig = true
+    }
+
     signingConfigs {
         if (releaseStoreFile != null && releaseStorePassword != null && releaseKeyAlias != null && releaseKeyPassword != null) {
             create("release") {

app/lint.xml

@@ -3,14 +3,21 @@
   Android Lint policy.
 
   CI runs `./gradlew lint` on every pull request and the job fails on lint *errors*.
-  Warnings are deliberately left as warnings for now: the pinch-zoom and word-wrap
-  deletions (prework items 3 and 4) and the P3/P4 refactor are about to move several
-  hundred lines, and fighting the linter through that at the same time is not worth it.
-  Revisit `warningsAsErrors` once P3 has landed.
+  Warnings are deliberately left as warnings for now; turning on `warningsAsErrors` is
+  planned.
 
   Anything suppressed here needs a reason next to it.
 -->
 <lint>
     <!-- Fires on Compose-held state that never touches LiveData nullability. -->
     <issue id="NullSafeMutableLiveData" severity="ignore" />
+
+    <!--
+      Translations are contributed by the community in separate PRs, so a feature PR may add
+      strings ahead of their translations. Android falls back to the default (en) string at
+      runtime, so an incomplete locale is a warning rather than a build-failing error.
+      ExtraTranslation stays an error: a translation of a string that no longer exists is stale,
+      and is deleted along with the string.
+    -->
+    <issue id="MissingTranslation" severity="warning" />
 </lint>

app/src/main/res/resources.properties

@@ -0,0 +1 @@
+unqualifiedResLocale=en-US