On Abbrev popup, these strings are hardcoded, not extracted from Bundle,

"Abbreviation:"
" for expansion]"

These are defined in

./editor/codetemplates/src/org/netbeans/lib/editor/codetemplates/CodeTemplateCompletionItem.java

            // Append abbreviation
            htmlText.append("<br>Abbreviation: &nbsp;"); // NOI18N
            htmlText.append(toHtmlText(codeTemplate.getAbbreviation()));
            htmlText.append("&nbsp; ["); // NOI18N
            // Append expansion keystroke
            String mimeType =
CodeTemplateApiPackageAccessor.get().getOperation(codeTemplate).getMimeType();
            htmlText.append(AbbrevSettings.get(mimeType).getExpandKeyStrokeText());
            htmlText.append(" for expansion]</html>"); // NOI18N
            return htmlText.toString();