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":
I added Fix submitter as assignee because this will ease queries and bug tracking.