To design a GUI that supports multiple languages:

1. Plan for internationalization (I18N) from the start.

2. Use Unicode character encoding for text.

3. Separate text from code using resource files or databases.

4. Design flexible layouts to accommodate varying text lengths.

5. Use language-neutral icons and graphics.

6. Format dates, times, and numbers according to local conventions.

7. Support right-to-left (RTL) and left-to-right (LTR) text directions.

8. Test with pseudo-translations to identify layout issues.

9. Use machine translation or professional translation services.

10. Provide language selection options for users.

11. Consider cultural differences in color schemes, imagery, and functionality.

12. Use internationalization frameworks or libraries.

Best practices:

1. Keep text short and concise.

2. Avoid hardcoded text.

3. Use placeholders for dynamic text.

4. Support font fallbacks for missing characters.

5. Test with different languages and scripts.

Tools and technologies:

1. Unicode and UTF-8 encoding

2. Resource files (e.g., .po, .resx)

3. Internationalization frameworks (e.g., gettext, ICU)

4. Translation management tools (e.g., Transifex, Crowdin)

5. GUI design tools with I18N support (e.g., Qt, wxWidgets)

By following these guidelines, you can create a GUI that effectively supports multiple languages and provides a great user experience worldwide.