My working environments for LanguageTool 3.8 are 64-bit Windows 7 Pro SP1 with Java Version 8 Update 144 and LibreOffice 5.3.4
… and …
64-bit Linux Mint 18.2 with openjdk-8-jre and LibreOffice 5.1.6.
I have never in years of trying been able to get LanguageTool working in LibreOffice. To test my installation, I navigated to https://languagetool.org/ and copied the sample text on display there and pasted it into LibreOffice text documents. I highlighted the text and opened the menu item Tools > LanguageTools > Check Text. Nothing happens but a plain-vanilla LibreOffice spell check. The grammar issues called out on your website are not highlighted in LibreOffice. I get the same absence of results in both Windows and Linux. In short, I have no evidence that the extension is functioning at all.
Since I have no screen shots, I don’t even know what it is supposed to look like when it does its job.
My wife desperately wants a grammar checker and is angry with me for not providing her one, and I am at a loss. [I see that the Firefox extension deals with the indicated errors in your sample text, but I don’t have so much as a picture of what is supposed to happen in LibreOffice.]
What am I doing wrong?