Originally Posted by PoP
Counting from the "MOBI" character string at offset 16 and adding 76 one finds 3 fields of 4 bytes each in your attached screen capture:
at offset 92 x'0009' this is the language the book is written into (english),
at offset 96 x'0009', for dictionaries this is the language you are translating from (english) and,
at offset 100 x'0009' the language you are translating to (english) meaning, I guess, this is not a translation but a definition dictionary.
thank you very much. I succeed understand this wiki said https://wiki.mobileread.com/wiki/MOBI#MOBI_Header
and I also found why '09' meaning English, because it's Locale IDs Assigned by Microsoft, find more at this