I just looked. In this case, it is just string translations.

In the version I'm looking at there are 27,470 .strings files totaling 69 MiB, but they take up 155.9 MiB of disk space due to the 4 KiB filesystem block size.

The keys for the strings take up 39% of the space while the values take up 61%. About 12% of translations are duplicated (the word "Cancel" is translated like 53 times)

So 55% of the space used for strings localization is just pure waste due to having so many small files. The long keys are rather wasteful too and about 12% of the translations are duplicated (i.e. the word "Cancel" is translated 50+ times per language).

Some of this is arguably Apple's fault. Their whole .string file per table per language is incredibly space inefficient by default.