Language definition is the file structure that is used by D3 to perform case insensitive compares according to other language definitions.
| 4 bytes | Contains the string 'LANG' (not byteswapped or NULL terminated). |
| 4 bytes | Language tag number, which is unique to each language. It must not be zero. The Cyrillic version is numbered 1. |
| 4 bytes | File version. All initial versions are 1. |
| 4 bytes | D3 internal date of last file update. |
| 16 bytes | Contains the language tag name (same as the file name) with a NULL terminator. |
| 128 bytes | Reserved. |
| 256 bytes | Corresponds to the convert to uppercase table. |
| 256 bytes | Corresponds to the get character information table. |
| 256 bytes | Corresponds to the convert to lowercase table. |