The correct English name for the language of the Slovak Republic (aka Slovakia) is "Slovak". The English version of LibreOffice (all versions) uses the INCORRECT adjective "Slovakian" - the adjective itself exists; nevertheless, the name of the language is "Slovak" - see e.g. http://oxforddictionaries.com/definition/Slovakia?q=slovakia. Please fix this.
Andras Timar committed a patch related to this issue. It has been pushed to "master": http://cgit.freedesktop.org/libreoffice/core/commit/?id=deb9b28697abe665f87076fc72fcee76212b68c8 fdo#46382 s/Slovakian/Slovak/
I added Fix submitter as assignee because this will ease queries and bug tracking.