• use lang for the language of the page, then the other parts of the page with a different language
• support different writing direction. Logical CSS properties help.
• handle text expansion with adaptive layouts. Avoid to truncate the text.
• apply a minimum width to avoid text shrinking in other languages. Also think about the height.
• readable typography is important
• make sure every user-facing string is translated such as alt-text, title or desc nodes in SVG.
• different languages have different word order, so avoid string templates
• ensure consistency of microcopy

  Microcopy is all the little bits of text that appear throughout the site: the nav links, the sidebar headings, the form field labels, stuff like that. When microcopy is written and used consistently, the site layout becomes much more predictable, and users won't have to guess

It means the atoms and some molecules in atomic design.