This label seems i18ned, but real string,
"Building" is not in bundle resource file.
When I run netbeans with Bundle debug mode,
it reported that label, "Building" is come from
file:core/src/org/netbeans/core/projects/Bundle_ja.properties,
line, 22.

But, line 22 is ...

| % cat -n
core/src/org/netbeans/core/projects/Bundle_ja.properties
| tail +22
|     22   CTL_HomeFile={0}
|     23   # CTL_UserFile={0}
|     24   CTL_UserFile={0}


to reproeuce:
  Tool -> Option