Perhaps I misunderstand something, but some entries in translatewiki's FallbackSettings.php are quite odd:
There are some languages there that already have their own core Messages*.php file and Names.php entry, like be-tarask, br, kab, etc. Are they supposed to be there at all?
For some of them the fallback settings are different from the corresponding Messages*.php file, for example kab. Is this right?
Some entries are just plain odd. Why, for example, is roa-rup defined as a fallback for br?
Some languages there have a "bigger" language before a "smaller" one, which may be closer linguistically. By "bigger" I mean "having more translations". One example is addressed in https://gerrit.wikimedia.org/r/#/c/416347/ : for the Quechuan languages, Spanish comes before other Quechuan languages. Is this right?