Spellcheck is enabled in classic Yandex.Browser for the operating system's default language.
To set the spellcheck language:
An incorrectly typed word is underlined with a wavy red line. You can correct it manually, or open the context menu to select one of the spellings suggested by the browser.
If you need to check the spelling of a word that isn't in the same language as the browser interface:
Now any spelling mistakes in the selected language will be underlined with a red wavy line.
To disable or enable spellcheck: