use translation string for clipboard pasting prompt

pd/nw/locales/en/translation.json

@@ -243,6 +243,7 @@
     "devtools_tt": "Show the DevTools window (for debugging)"
   },
   "canvas": {
+    "paste_clipboard_prompt": "Warning: you are about to paste Pd code that came from somewhere outside of Pd. Do you want to continue?",
     "save_dialog": {
       "yes": "Yes",
       "yes_tt": "Write the changes to file before closing the patch",

pd/nw/pd_canvas.js

@@ -64,7 +64,7 @@ function might_be_a_pd_file(stuff_from_clipboard) {
 }
 
 function permission_to_paste_from_external_clipboard() {
-    return global.confirm("Warning: you are about to paste Pd code that came from somewhere outside of Pd. Do you want to continue?");
+    return global.confirm(l("canvas.paste_clipboard_prompt"));
 }
 
 function nw_window_focus_callback() {