as long as the non-ASCII characters in the URL are properly escaped the Twitter Card shows up
the problem is, the Twitter web interface replaces the escape sequences with the corresponding UTF-8 characters, which makes the URL look like
The first URL is fine for Twitter, as it’s able to fetch the meta information from the page.
The second one is completely ignored, and the Card Validator complains about the invalid URL. I accept the point, that the URL is maybe mailformed. What I find problematic is that the URL originally passed to Twitter is actually correct, it’s the web interface which replaces escape sequences.
Double escaping characters seems like an extremely ugly workaround.