Indeed there's no good reason to restrict the word length, so I removed the restriction - please update to the newest version.
One thing: while testing the change, I noticed that it doesn't work with alphabets other than English. I hastily added support for Japanese, Chinese and Russian, but I'm not sure it works very well (it may have problems detecting where one word ends and another begins). If you encounter any issues, please report them via https://github.com/ainzzorl/wordhighlighter/issues.
