After the default installation of LibO_3.5.4_Win_x86_install_multi.msi and help pack LibO_3.5.4_Win_x86_helppack_en-GB, choosing Help (or pressing F1) goes to the help web site instead of bringing up the local help window.
I only found out from posting on the forum that this is because all language settings EXCEPT User Interface were set to English GB, but the User Interface language was set to English US. When I changed this to English GB, the help window came up correctly.
I regard this as an installation bug, since no-one installing Libre Office for the first time is going to spot this without advice.
(Sorry, I couldn't see where to set the I10n keyword - maybe that will come up when I submit.)
It never happens in my case (There is only one German language ;) )
I CCed the localization fixes / l10n tools expert.
Maybe he knows, where to tweak....
*** This bug has been marked as a duplicate of bug 39325 ***