Well, "interpreting" means reverse engineering and hacking in those cases.
You first have to learn how data are packed. This can be relatively easy or hard depending on how they are packed and if this happens using existing algorithms (with minor modifications or without modifications at all) or using new algorithms (and how hard it is to interpret them).
Then you have to use an existing unpacker or, most of the time, make your own.
Lastly you have to re-pack the modified/replaced data either by using the same algorithm(s) the game uses or by making you own algorithm(s).
Examples of the above steps are game hacks and translations.
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