Setting up and using the Lang attribute appropriately will assist with accessibility and better UX through all types of devices. Google said they ignore the Lang attribute for indexation purposes and instead they use hreflang, but that doesn’t mean they evaluate the websites accessibility and UX.
The standard reads
The lang (or sometimes the xml:lang ) attribute specifies the natural language of the content of a web page. An attribute on the html tag sets the language for all the text on the page. If part of the page uses text in a different language, you can add a language attribute with a different value to the element that surrounds that content.
You can define the Lang attribute for he whole page and then define each text different Lang attribute in another language. follow this instruction.
Following those recommendation will help you to have a cleaner HTML code and better overall webpage quality and it might help you with better SEO.