这是因为你有2规则，第一个先匹配（因为它比第二个更普遍）。

It's because you have 2 rules, and the first one matches first (as it is more general than the second).

在所有的第二甚至不检查词典。

The second doesn't even check for dictionary at all.

第二个条件应该是：

RewriteRule ^dictionary/([a-zA-Z])$ dictionary.php?letter=$1