Need A Help with .md5 and .addon files

[El.Amigos]

can anyone explain me how fitgirl is able to launch .addon files after checking .md5 files

for e.g. for any language say French there are two hash checksum files
Namely
Fitgirl.md5
and
French.md5

So the point is, after checking verify game files
How does this french.addon automatically checks french game files after checking common game files using Fitgirl.md5