An interface can have every translation and still fail at multilingual support. Words grow longer, accents extend higher and line breaks move. The container is unchanged, but the content no longer has the same shape.
Do not wait until design is finished to insert translations. Compare languages while building headings and buttons. Test the longest label on a narrow screen. If making a button fit requires removing the main meaning, reconsider its layout first.
For Vietnamese, inspect accents in large headings and the spacing between lines. For dense Chinese characters, outline effects can become busy with some fonts and sizes. Languages do not need identical decoration when that harms readability.
Numbers and dates need localisation too. Keep numeric values separate from display strings, then format for the language. Allow a long unit to wrap sensibly rather than forcing the row beyond its card.
A language switch should keep readers on the equivalent page when it exists. Someone reading an article should not unexpectedly return to the homepage just because they want another language.
Try a page with a long heading, a metric card and several buttons. Check every language on a small screen, enlarge the text and navigate by keyboard. Shared design means shared character and principles, not forcing every sentence into a rigid mould.