diff --git a/plugin-designs/research-map-plus-grid/research-map-plus-grid.vue b/plugin-designs/research-map-plus-grid/research-map-plus-grid.vue
index aac865d90..e1d3a45cb 100644
--- a/plugin-designs/research-map-plus-grid/research-map-plus-grid.vue
+++ b/plugin-designs/research-map-plus-grid/research-map-plus-grid.vue
@@ -444,7 +444,13 @@ function pushToChildren() {
     // every push. MEASURED: the map stayed English on a live en->ar switch while the composite
     // around it changed. The leaf's own chain is fully reactive and was never at fault — it is
     // reactive to its own prop, and its prop was frozen.
-    if (hostLang.value) cfg.lang = hostLang.value
+    // BOTH KEYS, and `locale` is the one that decides. Every reader takes locale FIRST and falls
+    // back to lang — ProfileLoader.vue:189 and people-groups-grid.vue:273/380 all read
+    // `config.locale || config.lang`. Writing only `lang` is therefore correct exactly while no
+    // child config carries a `locale`, and silently stops working the day one does: a stale locale
+    // from a boot copy or a host-list path would shadow every fresh lang we push, forever. Writing
+    // both keeps the two in step whatever put them there.
+    if (hostLang.value) { cfg.lang = hostLang.value; cfg.locale = hostLang.value }
     map.setAttribute('profile-config', JSON.stringify(cfg))
   }
   const grid = rootEl.querySelector('people-groups-grid')
@@ -461,8 +467,9 @@ function pushToChildren() {
     if (hostLang.value) {
       let gcfg = {}
       try { gcfg = JSON.parse(grid.getAttribute('profile-config') || '{}') } catch (_) { gcfg = {} }
-      if (gcfg.lang !== hostLang.value) {
+      if (gcfg.lang !== hostLang.value || gcfg.locale !== hostLang.value) {
         gcfg.lang = hostLang.value
+        gcfg.locale = hostLang.value
         grid.setAttribute('profile-config', JSON.stringify(gcfg))
       }
     }