I have installed 
```sh
sudo apt-get install default-jre
sudo apt-get install icedtea-plugin
```
following [install Java on Ubuntu][1].
I tried [this answer][2] after that tried to follow the steps [language tool HTTPS server][3]
The only difference wrt to [the above answer][2] is that I have kept the language tool in my home folder rather than in opt. Trying to run the Language tool server results in

[![Trying to run the Language tool server][4]][4]
and this is the 

Running
```sh
curl --data "language=en-US&text=a simple test" http://localhost:8081/v2/check
```
results in
```sh
{"software":{"name":"LanguageTool","version":"5.4",
"buildDate":"2021-06-25 10:24:16 +0000","apiVersion":1,
"premium":false,
"premiumHint": "You might be missing errors only the Premium version can find. 
Contact us at support<at>languagetoolplus.com.",
"status":""},"warnings":{"incompleteResults":false},
"language":{"name":"English (US)","code":"en-US",
"detectedLanguage":{"name":"French","code":"fr","confidence":0.815771}},
"matches":[{"message":"This sentence does not start with an uppercase letter.","shortMessage":"",
"replacements":[{"value":"A"}],
"offset":0,"length":1,
"context":{"text":"a simple test","offset":0,"length":1},"sentence":"a simple test",
"type":{"typeName":"Other"},
"rule":{"id":"UPPERCASE_SENTENCE_START",
"description":"Checks that a sentence starts with an uppercase letter",
"issueType":"typographical","category":{"id":"CASING","name":"Capitalization"}},
"ignoreForIncompleteSentence":true,"contextForSureMatch"
```
Similarly going to
[http://localhost:8082/v2/check?language=en-US&text=my+text][5]

leads to

```json
{"software":{"name":"LanguageTool","version":"5.4",
"buildDate":"2021-06-25 10:24:16 +0000",
"apiVersion":1,"premium":false,
"premiumHint": "You might be missing errors only the Premium version can find. Contact us at support<at>languagetoolplus.com.",
"status":""},"warnings":{"incompleteResults":false},
"language":{"name":"English (US)",
"code":"en-US",
"detectedLanguage":{"name":"English (US)","code":"en-US",
"confidence":0.65618557}},
"matches":[{"message": "This sentence does not start with an uppercase letter.",
"shortMessage":"",
"replacements":[{"value":"My"}],
"offset":0,"length":2,
"context":{"text":"my text","offset":0,"length":2},
"sentence":"my text","type":{"typeName":"Other"},
"rule":{"id":"UPPERCASE_SENTENCE_START",
"description":"Checks that a sentence starts with an uppercase letter",
"issueType":"typographical",
"category":{"id":"CASING","name":"Capitalization"}},
"ignoreForIncompleteSentence":true,"contextForSureMatch":-1}]}
```
Strangely the standalone version of the Language tool  works
On typing 
```java -jar languagetool.jar```
in the terminal, we have
[![standalone language tool][6]][6]

My TeX studio settings
[![Texstudio setting][7]][7]


And the output of Texstudio> Help> check Language tool is 

which java: /usr/bin/java

JAVA: java -version
openjdk version "11.0.11" 2021-04-20
OpenJDK Runtime Environment (build 11.0.11+9-Ubuntu-0ubuntu2.18.04)
OpenJDK 64-Bit Server VM (build 11.0.11+9-Ubuntu-0ubuntu2.18.04, mixed mode)

Real-time checking is enabled.
Grammar checking is enabled.

Tries to start automatically.

LT current status: working

LT-URL: http://localhost:8081/v2/check


  [1]: https://askubuntu.com/a/88058/707756
  [2]: https://tex.stackexchange.com/a/401103/129388
  [3]: https://dev.languagetool.org/http-server.html
  [4]: https://i.stack.imgur.com/T3J82.png
  [5]: http://localhost:8082/v2/check?language=en-US&text=my%20text
  [6]: https://i.stack.imgur.com/YuXCG.png
  [7]: https://i.stack.imgur.com/LRM4A.png