What you need to know
The lang attribute tells assistive technology how to pronounce words and lets browsers apply language-specific behavior. It is especially important for multilingual sites where a page or a section may use a different language.
How to apply it
Set lang on the root html element to the primary language of the page, such as en or bn. Mark short passages in another language on the element that contains them when pronunciation matters.
Common mistake to avoid
Do not set a language code based on the developer's preference if the page content is in another language. Keep metadata, visible text, and the declared language aligned.