Answer architecture round 5: the shipped packages are enus, svse, geose, geous and misc, each holding its files at its root under its manifest's namespace, and the errors use the wording a bench of the Audience chose

data/en_US/fs.go

@@ -1,9 +0,0 @@
-// Package en_US is fejkdata's en_US locale module.
-package en_US
-
-import "embed"
-
-// FS holds the en_US categories and the module's manifest; pass it to fejkdata.WithDataFS.
-//
-//go:embed en_US .fejkdata.json
-var FS embed.FS

data/enus/.fejkdata.json

@@ -23,5 +23,6 @@
 		"en_US.version": {"paths":["","n","pre","suffix"]},
 		"en_US.word": {"paths":[""]}
 	},
-	"reads": ["github.com/larvit/fejkdata/data/geo/US"]
+	"namespace": "en_US",
+	"reads": ["github.com/larvit/fejkdata/data/geous"]
 }

data/enus/fs.go

@@ -0,0 +1,9 @@
+// Package enus is fejkdata's en_US locale module, whose categories are en_US.*. Its address reads geous's places.
+package enus
+
+import "embed"
+
+// FS holds the module's categories and its manifest; pass it to fejkdata.WithDataFS.
+//
+//go:embed *.json *.tsv .fejkdata.json
+var FS embed.FS

data/geo/SE/fs.go

@@ -1,9 +0,0 @@
-// Package SE is fejkdata's Swedish geography module.
-package SE
-
-import "embed"
-
-// FS holds the geo.SE categories and the module's manifest; pass it to fejkdata.WithDataFS.
-//
-//go:embed geo .fejkdata.json
-var FS embed.FS

data/geo/US/fs.go

@@ -1,9 +0,0 @@
-// Package US is fejkdata's US geography module.
-package US
-
-import "embed"
-
-// FS holds the geo.US categories and the module's manifest; pass it to fejkdata.WithDataFS.
-//
-//go:embed geo .fejkdata.json
-var FS embed.FS

data/geose/.fejkdata.json

@@ -6,5 +6,6 @@
 		"geo.SE.postal-code": {"parent":"locality","paths":["","code","locality"]},
 		"geo.SE.region": {"paths":["","code","municipality","municipality.code","municipality.locality","municipality.locality.lat","municipality.locality.lon","municipality.locality.municipality","municipality.locality.name","municipality.locality.population","municipality.locality.postal-code","municipality.locality.postal-code.code","municipality.locality.postal-code.locality","municipality.locality.street","municipality.locality.street.locality","municipality.locality.street.name","municipality.locality.street.segments","municipality.name","municipality.population","municipality.region","name","population","timezone"]},
 		"geo.SE.street": {"parent":"locality","paths":["","locality","name","segments"]}
-	}
+	},
+	"namespace": "geo.SE"
 }

data/geose/fs.go

@@ -0,0 +1,9 @@
+// Package geose is fejkdata's Swedish places module, whose categories are geo.SE.*.
+package geose
+
+import "embed"
+
+// FS holds the module's categories and its manifest; pass it to fejkdata.WithDataFS.
+//
+//go:embed *.json *.tsv .fejkdata.json
+var FS embed.FS

data/geous/.fejkdata.json

@@ -6,5 +6,6 @@
 		"geo.US.postal-code": {"parent":"locality","paths":["","addresses","code","locality"]},
 		"geo.US.region": {"paths":["","abbr","code","municipality","municipality.code","municipality.locality","municipality.locality.code","municipality.locality.lat","municipality.locality.lon","municipality.locality.municipality","municipality.locality.name","municipality.locality.population","municipality.locality.postal-code","municipality.locality.postal-code.addresses","municipality.locality.postal-code.code","municipality.locality.postal-code.locality","municipality.locality.street","municipality.locality.street.addresses","municipality.locality.street.locality","municipality.locality.street.name","municipality.name","municipality.population","municipality.region","name","population","timezone"]},
 		"geo.US.street": {"parent":"locality","paths":["","addresses","locality","name"]}
-	}
+	},
+	"namespace": "geo.US"
 }

data/geous/fs.go

@@ -0,0 +1,9 @@
+// Package geous is fejkdata's US places module, whose categories are geo.US.*.
+package geous
+
+import "embed"
+
+// FS holds the module's categories and its manifest; pass it to fejkdata.WithDataFS.
+//
+//go:embed *.json *.tsv .fejkdata.json
+var FS embed.FS

data/misc/.fejkdata.json

@@ -20,5 +20,6 @@
 		"misc.tld": {"paths":["","tld","type","unicode"]},
 		"misc.useragent": {"paths":["","browser","device","os","ua"]},
 		"misc.uuid": {"paths":["","variant"]}
-	}
+	},
+	"namespace": "misc"
 }

data/misc/fs.go

@@ -1,9 +1,9 @@
-// Package misc is fejkdata's misc module.
+// Package misc is fejkdata's locale-neutral module, whose categories are misc.*.
 package misc
 
 import "embed"
 
-// FS holds the misc categories and the module's manifest; pass it to fejkdata.WithDataFS.
+// FS holds the module's categories and its manifest; pass it to fejkdata.WithDataFS.
 //
-//go:embed misc .fejkdata.json
+//go:embed *.json *.tsv .fejkdata.json
 var FS embed.FS

data/modules.go

@@ -1,20 +1,19 @@
-// Package data lists every module fejkdata ships. A module's tree spells its namespace:
-// data/geo/SE embeds geo/SE/…, whose categories are geo.SE.*.
+// Package data lists every module fejkdata ships.
 package data
 
 import (
 	"io/fs"
 
-	"github.com/larvit/fejkdata/data/en_US"
-	"github.com/larvit/fejkdata/data/geo/SE"
-	"github.com/larvit/fejkdata/data/geo/US"
+	"github.com/larvit/fejkdata/data/enus"
+	"github.com/larvit/fejkdata/data/geose"
+	"github.com/larvit/fejkdata/data/geous"
 	"github.com/larvit/fejkdata/data/misc"
-	"github.com/larvit/fejkdata/data/sv_SE"
+	"github.com/larvit/fejkdata/data/svse"
 )
 
 //go:generate env REGENERATE=1 go test -run ^TestShippedManifestsAreCurrent$ ..
 
 // Modules returns every module fejkdata ships, to pass to fejkdata.WithDataFS.
 func Modules() []fs.FS {
-	return []fs.FS{en_US.FS, SE.FS, US.FS, misc.FS, sv_SE.FS}
+	return []fs.FS{enus.FS, geose.FS, geous.FS, misc.FS, svse.FS}
 }

data/sv_SE/fs.go

@@ -1,9 +0,0 @@
-// Package sv_SE is fejkdata's sv_SE locale module.
-package sv_SE
-
-import "embed"
-
-// FS holds the sv_SE categories and the module's manifest; pass it to fejkdata.WithDataFS.
-//
-//go:embed sv_SE .fejkdata.json
-var FS embed.FS

data/svse/.fejkdata.json

@@ -23,5 +23,6 @@
 		"sv_SE.version": {"paths":["","n","pre","suffix"]},
 		"sv_SE.word": {"paths":[""]}
 	},
-	"reads": ["github.com/larvit/fejkdata/data/geo/SE"]
+	"namespace": "sv_SE",
+	"reads": ["github.com/larvit/fejkdata/data/geose"]
 }