To help you write and spell in English, then, there's Grammarly, an extension for Google Chrome to help you avoid these kinds of mistakes.
Grammarly is designed to help you write professional emails, messages, and other texts in English; it can be especially useful if you use English for work or want to post something to a social network but first want to make sure there aren't any mistakes. Grammarly monitors everything you write on the browser to warn you of grammatical errors and misspellings.
This extension will help you write well on Gmail, Facebook, Twitter, LinkedIn, Tumblr, or any other site. When it detects an error, the Grammarly icon turns red. You can right-click on the word to see the correct spelling or phrasing.
Grammarly has an intelligent dictionary for spelling, grammar, and punctuation errors, and can check for mistakes in subject-verb agreement or usage of commas, periods, and apostrophes, for example.
The Pro version is free for 7 days.