The MindMeister web app supports multiple different languages, among them English, German, Danish, Dutch, French, Italian, Japanese, Korean, Portuguese, Russian, Spanish, Simplified Chinese and Traditional Chinese.
To change the language, simply scroll down on any page on mindmeister.com until you see the footer. There, you will see which language is currently being displayed. Click on the small triangle next to the displayed language to open the language menu and select a different one from the list.
(Note that the footer is not available while you're in the mind map editor.)
If you notice a problem with a translation or want to help us improve our translations, please don't hesitate to get in touch with our translation manager Silviu at email@example.com, or with the support team at firstname.lastname@example.org.