Thanks output of "ls -1" I see the file build-impl.xml is on top level as no such file should be there (I mean right after unzip of samples bundle you do not get it here).
What I suspect is that this file was originally in HelloI18N/nbproject/, which is the place it is looked for according the error message you get.
Once this file is back to its original location that should do way better, but you'll bump another (small) issue: the sample will refuse to start because the main class is not found: it is fixed in the SceneBuilder 2.0 GA build which we hope to get public soon, and for the time being you have to add an extra option on the command line and go with:
ant -Dplatforms.JDK_1.8.home=/usr -Dmain.class=helloi18n.Main -f HelloI18N/build.xml run
Let us know how it does !