应该是不同时代的规范问题。以下是从维基百科上节选的文字：
关于ß：
It was also in use for Latin during the Medieval and Renaissance time, until the 18th century. E.g.: clarißimus - clarissimus - the brightest; eße - ĕsse - to be; amavißet - amavisset and so on.
关于Æ：
In Classical Latin, the combination AE denotes the diphthong [ai̯], which had a value similar to the long i in fine as pronounced in most dialects of modern English. Both classical and present practice is to write the letters separately, but the ligature was used in medieval and early modern writings in part because æ was reduced to the simple vowel [ɛ] in the imperial period. In some medieval scripts, the ligature was simplified to ę, small letter e with ogonek, the e caudata. This form further simplified into a plain e, which may have influenced or been influenced by the pronunciation change. However, the ligature is still relatively common in liturgical books and musical scores.
关于Đ：
Đ was used in Medieval Latin to mark abbreviations of words containing the letter d. For example, hđum could stand for heredum "of the heirs". Similar crossbars were added to other letters to form abbreviations.
关于长S：
The long s was derived from the old Roman cursive medial s. When the distinction between majuscule (uppercase) and minuscule (lowercase) letter forms became established, toward the end of the eighth century, it developed a more vertical form. [...] The long s disappeared from new fonts rapidly in the mid-1790s, and most printers who could afford to do so had discarded older fonts by the early years of the 19th century.
Þ被视为拉丁字母。但是，真正的拉丁文用到过这个吗？楼主可以给我们举例。
[Tyzeka于2014-08-20 15:42编辑了帖子]
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