Index: /applications/editors/josm/plugins/wikipedia/src/org/wikipedia/gui/WikidataTagCellRenderer.java
===================================================================
--- /applications/editors/josm/plugins/wikipedia/src/org/wikipedia/gui/WikidataTagCellRenderer.java	(revision 34158)
+++ /applications/editors/josm/plugins/wikipedia/src/org/wikipedia/gui/WikidataTagCellRenderer.java	(revision 34159)
@@ -57,5 +57,7 @@
         ids.forEach(id ->
                 labelCache.computeIfAbsent(id, x ->
-                        CompletableFuture.supplyAsync(() -> WikipediaApp.getLabelForWikidata(x, Locale.getDefault())))
+                        CompletableFuture.supplyAsync(() -> WikipediaApp.getLabelForWikidata(x, Locale.getDefault()),
+                        // See #16204#comment:10 - Don't use ForkJoinPool#commonPool(), does not work with WebStart
+                        Utils.newForkJoinPool("wikipedia.wikidata.renderer.numberOfThreads", "wikidata-renderer-%d", Thread.NORM_PRIORITY)))
         );