According to the Texstudio manual, the standard distribution already has an English spellchecker. You perform a spell check by using the shortcut Ctrl+Shift+F7. Spell checking will start at the cursor position and not at the beginning of the document.
In addition, you may use a ‘magic comment’ in your TeX- source file:
% !TeX spellcheck = en_GB
If this comment is present in a file, the given language is automatically used for spell checks.
Use:
% !TeX spellcheck = en_US
if you prefer US spelling. You use this code in all .tex-files you want to spell check, i.e. both in the main file and in the chapter files, if your sources are divided in multiple chapters.
Remember, the percent sign is mandatory.
Section 1.4 in the manual has detailed information how to set up different languages and perform spell checks (and grammar checks).
I have the same problem. I found the way as follows: When you need to check Grammarly, copy the TeX to https://www.overleaf.com/ and you can also edit and run the TeX in there (online). Then the browser will check this for you. I think this is the best way right now. Or you can use the checker by Texstudio, they have it. But it is very very basic.
Best Answer
I am using TeXstudio with Language Tool under Windows 7 without any problems. The entry in the wiki is not valid for the newest version. You need to use the
languagetool.jar. Then everything should work. All the other files you mentionend, existed in previous version of the tool, but are now removed. See the changelog.