I have TexStudio 2.12.6 and LanguageTool 3.7.
The grammar checking does not work
Here is the screenshot of my configuration file:
Here si the output of Help-.>Check Language Tool
JAVA: C:\Program Files (x86)\Java\jre1.8.0_151\bin\java.exe -version
Real-time checking is enabled.
Grammar checking is enabled.
Tries to start automatically.
LT current status: error
Here is the output of http://localhost:8081/:
Error: You're using an old version of our API that's not supported anymore. Please see https://languagetool.org/http-api/migration.php
I have followed the instruction posted in your wiki, with link omitted due to your rules on new users, which specifically say:
Note You need TeXstudio 2.12.2 or later to work with LT 3.6 or later
P.S. LanguageTool 3.5 does not work either