The prefix number of the version indicates the language of the firmware:
2 English
3 Russian
4 Portuguese
5 Spanish - Latin display
15 Spanish - Cyrillic display
6 Turkish - Latin display
16 Turkish - Cyrillic display
7 Polish
8 Ukrainian
The second and third numbers indicate the version number.
Check out the Product Changes section in our Help Center to find out what the latest version is. Note the top section describes the Mobile App version and the second section describes the firmware version.