I am using LibreOffice version 188.8.131.52 in Linux openSUSE Leap 42.1. My system was installed with Portuguese (Brazil) as default language. I have installed also English and Russian as additional languages.
When using LibreOffice the user interface is in English. When I click on the pull down menu in Tools > Options > Language Settings > Language > User interface, the only options are English or Russian and I can not change it to Portuguese (Brazil).
All other language options In the menu (Locale setting, Decimal separator key, Default currency, Date acceptance patterns and Default language for documents) are Portuguese (Brazil).
I have uninstalled and then installed LibreOffice again, but the problem was not solved.