You can’t enter directly http://jp.ninafurfur.com/product/chanel-デカマトラッセ/ because in Japanese many people are not putting spaces between URLs and the rest of the text. If we allowed Japanese characters in URL paths, “http://example.com/testはおもしろいページだ” would be considered to be one long URL instead of a URL + some text. So you have to use the escaped version of the URL.
You say using the escaped version of the URL goes over the character limit of the tweet but it doesn’t. Any URL only takes 22 or 23 characters (22 for http, 23 for https) from the 140 characters limit, whatever the URL’s length.
To compute the real length of a tweet, you can use for example one of the twitter-text libraries:
They all allow you to get a tweet’s length or to check if a tweet is invalid or not.
