Thank you for clarifying it. We have a problem with Windows Vista on old versions of Family Tree Builder (build 18.104.22.1680 and below). The problem is that the default installation path is c:\program files\myheritage and users who accept the default on Vista may run into permissions problems later that prevent saving the program's configuration file. The symptom you are seeing is that the data language of the program is not being saved properly, but the same would apply to any non-default configuration setting you'd like to change. We solved this in newer versions by change the default installation folder on Vista to be away from c:\program files.
So my suggestion to you is the following: download the latest version of Family Tree Builder 3.0 from our site, which is 22.214.171.1246 at the moment, from here. After doing that, uninstall your Family Tree Builder. Don't worry, it will not delete data, it will only remove program files. Then install the new version 126.96.36.1996 and be sure to install it into c:\myheritage and not c:\program files\myheritage
This should address your problem and you will find that the new version also runs much faster on Vista. Please try this and update here with the outcome.