Adding a new external dictionary

I’m trying to use an external dictionary to our Language Tool.
Is this possible accessing an external dictionary?

Also, i need to know is there a possibility to activate spell check in new English() class.

Not directly, but you can add words to org/languagetool/resource/en/hunspell/spelling.txt to get them accepted by the spell checker.

Just use the sub classes like BritishEnglish instead of English and you’ll get spell checking automatically.