In what sense "it offers you" the update?

Maybe you just got notified, after starting OpenOffice, that a newer version of the German dictionary is available. This is normal, since the Dutch version includes several dictionaries (Dutch, but also English, French and German).

If this is your case, everything is working as expected and this is not a bug. Otherwise please give more information.

"AOO 4.0.1 – NL /  NL [AOO401m3(Build:9712) - Rev. 1520285 2013-09-05 13:52:01]" on German WIN7 Home Premium (64bit)", Common 4.0 User Profile
Leads me to <http://www.openoffice.org/de/?utm_source=AOO4_0_0_de&utm_medium=Client&utm_campaign=Upgrade>, what might confirm the problem. 

More research required ...

NOT Reproducible with "AOO 4.0.1 RC3 – German UI / German locale [Rev. 1524958 2013-09-20 11:40:29]" on German WIN7 Home Premium (64bit)", “historic” 4.0 User Profile used for all predecessor versions, where update notification leads to 
<http://www.openoffice.org/fr/Telecharger/?utm_source=AOO4_0_1_fr&utm_medium=Client&utm_campaign=Upgrade>

needhelp:
I wonder where it is defined to what locale page user will be leaded ...

@Andrea:
I think this has nothing to do with dictionaries or so. Probably user has installed en_us + Dutch Language pack

@Gijzo:
Please contribute more precise information!

@Rainer: to see how it works, open
http://svn.apache.org/viewvc/openoffice/updates-site/trunk/aoo401/check.Update?view=markup

This is what we serve to OpenOffice 4.0.1 when it looks for updates. Then OpenOffice parses the file and determines if there is a newer version and where to get it (it works similarly for 4.0, see SVN; and we have files for other versions too, but they are elsewhere in SVN).

All Dutch links for 4.0.1 seem to be correctly pointing to the NL site.

As for langpacks: if I test with OpenOffice 4.0.1 Italian with an active English language pack (i.e., menus set to English), I get the update links of the base version (i.e., 4.1.0 Italian). So language packs do not affect the selection.

Unless you see something wrong in the update feed, we'll have to conclude that we can't reproduce this (or that we need more info from the reporter).

(In reply to Andrea Pescetti from comment #4)
I think I understand that more or less, and currently I don't think that the problem is in the code behind the link. 

Now the question is how the AOO version decides whether it is "OpenOffice_4_nl" of whether "OpenOffice_4_de" or soemthing else. 

I installed French language pack and checked updates from active French UI with Locale and default document language = French. Update info lead me to German <http://www.openoffice.org/de/?utm_source=AOO4_0_0_de&utm_medium=Client&utm_campaign=Upgrade>. 

So it seems that the main installer determines the Language of the AOO installation?

@Gijzo:
If you use WINDOWS:
In 'WINDOWS -> System Settings -> Programs and functions' (Free translation from German' after rightlick on the columns heading you can enable a column "Source". I am pretty sure that your AOO 4.0.1 source file will end with " ..._de"?

@Gijzo:
Alternatively you can look into the program folder, the readme.txt should show the language of the main installer.

No news from OP