AS stated by DeanK
"On Windows XP Pro, using LibreOffice English version (en-GB):
go to C:\Program Files\LibreOffice 3.5\Help, there will be a en-BG (English version) folder. Select all the files in the folder, cut and paste it into the C:\Program Files\LibreOffice 3.5\Help folder, delete the en-GB folder(now empty).
Then go to Control Panel and click on “Application/Product Installer” (I don’t remeber the right name beacuse I’ve Italian language installed; anyway it’s the “box with a little CDROM beside”!). Look for your LibreOffice release installed, then click on it to MODIFY-ADJUST the installation.
Once LibreO. installer started and you choosed the modify choice, it will be prompted a tree with all the feature still present and those you might need. Go inside the “User Interface Language Support Branch” and choose ENGLISH UK. Then confirm and go on with the install interface (wait untill it’s finished).
I made some experiments and there’s no need to uninstall and reinstall all the application, unless some chaos has been made before to start our changes.
Many Thanks to DeanK!!!
This helped me because LibreO. 3.5.4.2 comes with UI-English(US) by default in
its installation process, without any other UI-Language selected; when I ran the installer I didn’t configured UI-Language.