1_ First of all, you have to open the options menu of the LibreOffice Writer.
You can find this menu in "Tools".
2_ After that, in the options menu, you will have to select the "Language Settings" and open "Languages". There, you'll change the program's language.
3_ Here we will have to select the language that we want for the program. You'll can choose between different languages. When you have choosed the language you'll have to press "OK" and the settings will be saved.
And that's all. You've changed the program's language. This settings are aviable in every LibreOffice programs.
Mr. Orchero.