I really hated having to switch languages, when I switched to writing from Hungarian and English. Many times I was writing mail, or working on an article in English, when a Hangouts message popped up where I had all my words underlined by the English spellchecker.
Finally after over a year in progress, guys at Google managed to add the feature to Chrome.
Too bad it’s quite hidden at the moment, and even though I followed it on the bug tracker it didn’t appear in my basic settings panel.
(NB: Doesn’t work on Android, or IOS)