Do not allow installation of plugins with the same ID (#7870)

i18n/en.json

@@ -3558,6 +3558,14 @@
     "id": "app.plugin.activate.app_error",
     "translation": "Unable to activate extracted plugin. Plugin may already exist and be activated."
   },
+  {
+    "id": "app.plugin.install.app_error",
+    "translation": "Unable to install plugin."
+  },
+  {
+    "id": "app.plugin.install_id.app_error",
+    "translation": "Unable to install plugin. A plugin with the same ID is already installed."
+  },
   {
     "id": "app.plugin.config.app_error",
     "translation": "Error saving plugin state in config"
@@ -3592,7 +3600,7 @@
   },
   {
     "id": "app.plugin.mvdir.app_error",
-    "translation": "Unable to move plugin from temporary directory to final destination"
+    "translation": "Unable to move plugin from temporary directory to final destination. Another plugin may be using the same directory name."
   },
   {
     "id": "app.plugin.not_installed.app_error",