An .acl file is an AutoCorrect List file. These are the files where Office stores unformatted auto-correct entries. (Formatted entries for Word are stored in the Normal.dot file).
The number in the filename (xxxx) refers to the language id of the autocorrections.
The special number 0127 (MSO0127.acl) is for Math AutoCorrect entries.
The files seem to be encoded in UTF 16, little endian with some byte-clutter that help to index the entries.