The use of foreign language characters is not supported in Mingle. Mingle has not been internationalized or localized for non-English and English is the only supported language. Foreign language characters can still be used as plain text in card descriptions.
Here are a few instances where non-English characters are known to cause issues:
1. Non-English characters used as card properties
2. Non-English characters used as card types
3. Non-English characters used in macros
4. Non-English characters in LDAP username
Internationalization and support for non-English languages has been added to our backlog to be prioritized in future releases. Your feedback on this feature and/or feedback on Mingle itself will aid us in building a better product and user experience.