diff --git a/Cargo.lock b/Cargo.lock
index 03a69fc5d76..66f43bbf7b6 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -3135,6 +3135,7 @@ dependencies = [
  "databake",
  "displaydoc",
  "postcard",
+ "potential_utf",
  "rand",
  "serde",
  "serde_json",
diff --git a/provider/source/tests/dnametest.rs b/provider/source/tests/dnametest.rs
new file mode 100644
index 00000000000..9e15171856c
--- /dev/null
+++ b/provider/source/tests/dnametest.rs
@@ -0,0 +1,226 @@
+// This file is part of ICU4X. For terms of use, please see the file
+// called LICENSE at the top level of the ICU4X source tree
+// (online at: https://github.com/unicode-org/icu4x/blob/main/LICENSE ).
+
+use std::collections::{BTreeMap, BTreeSet};
+
+use icu::locale::{
+    fallback::{LocaleFallbackConfig, LocaleFallbackPriority, LocaleFallbacker},
+    locale, LocaleExpander,
+};
+use icu_experimental::displaynames::provider::RegionDisplayNamesV1;
+use icu_provider::prelude::*;
+use icu_provider_source::SourceDataProvider;
+use litemap::LiteMap;
+use ndarray::{Array2, Axis};
+use tinystr::TinyAsciiStr;
+use zerotrie::ZeroTrieSimpleAscii;
+
+#[test]
+fn dnametest() {
+    let provider = SourceDataProvider::new_custom()
+        .with_cldr(&std::path::PathBuf::from(
+            "/home/sffc/lib/cldr-46.0.0-json-full",
+        ))
+        .unwrap();
+
+    let locales: BTreeMap<DataIdentifierCow<'_>, usize> =
+        IterableDataProvider::<RegionDisplayNamesV1>::iter_ids(&provider)
+            .unwrap()
+            .into_iter()
+            .enumerate()
+            .map(|(i, v)| (v, i))
+            .collect();
+
+    let payloads: BTreeMap<DataIdentifierCow, DataPayload<RegionDisplayNamesV1>> = locales
+        .keys()
+        .map(|locale| {
+            let payload = provider
+                .load(DataRequest {
+                    id: locale.as_borrowed(),
+                    ..Default::default()
+                })
+                .unwrap()
+                .payload;
+            (locale.clone(), payload)
+        })
+        .collect();
+
+    let unique_names: Vec<&str> = payloads
+        .values()
+        .flat_map(|v| v.get().names.iter_values())
+        .collect::<BTreeSet<_>>()
+        .into_iter()
+        .collect();
+    let unique_names_required_bits = (unique_names.len() as f64).log2().ceil() as usize;
+    println!("unique_names: {} ({unique_names_required_bits})", unique_names.len());
+
+    let regions: BTreeSet<TinyAsciiStr<3>> = payloads
+        .get(&DataIdentifierCow::from_locale(locale!("en").into()))
+        .unwrap()
+        .get()
+        .names
+        .iter_keys()
+        .map(|s| s.try_into_tinystr().unwrap())
+        .collect();
+
+    let expander = LocaleExpander::try_new_common_unstable(&provider).unwrap();
+    let fallbacker = LocaleFallbacker::try_new_unstable(&provider).unwrap();
+    let mut config = LocaleFallbackConfig::default();
+    config.priority = LocaleFallbackPriority::Script;
+    let fallbacker = fallbacker.for_config(config);
+
+    let script_locales: BTreeMap<DataIdentifierCow, usize> = locales
+        .keys()
+        .filter_map(|locale| {
+            let mut fallback_iterator = fallbacker.fallback_for(locale.locale);
+            loop {
+                let parent_locale = fallback_iterator.get();
+                if parent_locale.is_unknown() {
+                    println!("Didn't find script parent for: {:?}", locale.locale);
+                    break None;
+                }
+                if parent_locale.language.is_unknown() && parent_locale.region.is_none() {
+                    break Some(DataIdentifierCow::from_locale(*parent_locale));
+                }
+                fallback_iterator.step();
+            }
+        })
+        .collect::<BTreeSet<_>>() // put in order
+        .into_iter()
+        .enumerate()
+        .map(|(a, b)| (b, a))
+        .collect();
+
+    let mut dense_matrix =
+        Array2::<Option<usize>>::default((locales.len() + script_locales.len(), regions.len()));
+
+    for (i, (_locale, payload)) in payloads.iter().enumerate() {
+        for (j, region) in regions.iter().enumerate() {
+            if let Some(name) = payload.get().names.get(&region.to_unvalidated()) {
+                let index = unique_names.binary_search(&name).unwrap();
+                dense_matrix[(i, j)] = Some(index);
+            }
+        }
+    }
+
+    for (i, script_locale) in script_locales.keys().enumerate() {
+        let i = i + locales.len();
+        let mut locale = script_locale.locale.into_locale();
+        expander.maximize(&mut locale.id);
+        expander.minimize_favor_script(&mut locale.id);
+        if let Some(k) = locales.get(&DataIdentifierCow::from_locale((&locale).into())) {
+            println!("Copying: {locale:?} to {:?}", script_locale.locale);
+            for (j, _region) in regions.iter().enumerate() {
+                dense_matrix[(i, j)] = dense_matrix[(*k, j)];
+            }
+        }
+    }
+
+    for (i, (locale, _payload)) in payloads.iter().enumerate() {
+        'j: for (j, _region) in regions.iter().enumerate() {
+            let Some(value) = dense_matrix[(i, j)] else {
+                continue;
+            };
+            let mut fallback_iterator = fallbacker.fallback_for(locale.locale);
+            loop {
+                fallback_iterator.step();
+                let parent_locale = *fallback_iterator.get();
+                if parent_locale.is_unknown() {
+                    break;
+                }
+                if let Some(k) = locales
+                    .get(&DataIdentifierCow::from_locale(parent_locale))
+                    .copied()
+                    .or_else(|| {
+                        script_locales
+                            .get(&DataIdentifierCow::from_locale(parent_locale))
+                            .map(|x| x + locales.len())
+                    })
+                {
+                    if let Some(parent_value) = dense_matrix[(k, j)] {
+                        if parent_value == value {
+                            dense_matrix[(i, j)] = None;
+                        }
+                        continue 'j;
+                    }
+                }
+            }
+        }
+    }
+
+    let large_small = dense_matrix.map_axis(Axis(1), |values| {
+        values.iter().filter(|v| v.is_some()).count()
+    });
+
+    for (i, locale) in locales.keys().chain(script_locales.keys()).enumerate() {
+        println!("{locale:<3}: {}", large_small[i]);
+    }
+
+    let locales_with_data: Vec<DataIdentifierBorrowed> = locales
+        .keys()
+        .chain(script_locales.keys())
+        .enumerate()
+        .filter(|(i, _)| large_small[*i] != 0)
+        .map(|(_, locale)| locale.as_borrowed())
+        .collect();
+    println!("locales_with_data: {}", locales_with_data.len());
+
+    let locales_only_zerotrie: ZeroTrieSimpleAscii<Vec<u8>> = locales_with_data
+        .iter()
+        .enumerate()
+        .map(|(i, locale)| (locale.to_string(), i))
+        .collect();
+    println!("locales_only_zerotrie: {}", locales_only_zerotrie.byte_len());
+
+    let regions_only_zerotrie: ZeroTrieSimpleAscii<Vec<u8>> = regions.iter().enumerate()
+        .map(|(i, locale)| (locale.to_string(), i))
+        .collect();
+
+    println!("regions_only_zerotrie: {}", regions_only_zerotrie.byte_len());
+
+    let sparse_map: LiteMap<String, usize> = locales
+        .keys()
+        .chain(script_locales.keys())
+        .enumerate()
+        .flat_map(|(i, locale)| {
+            let dense_matrix = &dense_matrix;
+            regions.iter().enumerate().filter_map(move |(j, region)| {
+                dense_matrix[(i, j)].map(|index| (format!("{locale}/{region}"), index))
+            })
+        })
+        .collect();
+    println!("sparse_map: {}", sparse_map.len());
+
+    let sparse_zerotrie: ZeroTrieSimpleAscii<Vec<u8>> =
+        sparse_map.iter().map(|(k, v)| (k, *v)).collect();
+    println!("sparse_zerotrie: {}", sparse_zerotrie.byte_len());
+
+    let dense_row_bit_size = regions.len() * unique_names_required_bits;
+
+    let mut num_dense_locales = 0;
+    let hybrid_sparse_map: LiteMap<String, usize> = locales
+        .keys()
+        .chain(script_locales.keys())
+        .enumerate()
+        .flat_map(|(i, locale)| {
+            let dense_matrix = &dense_matrix;
+            let row: Vec<(String, usize)> = regions.iter().enumerate().filter_map(move |(j, region)| {
+                dense_matrix[(i, j)].map(|index| (format!("{locale}/{region}"), index))
+            }).collect();
+            let inner_zerotrie: ZeroTrieSimpleAscii<_> = row.iter().map(|(k, v)| (k, *v)).collect();
+            if inner_zerotrie.byte_len() * 8 > dense_row_bit_size {
+                num_dense_locales += 1;
+                vec![(locale.to_string(), 0)].into_iter()
+            } else {
+                row.into_iter()
+            }
+        })
+        .collect();
+    println!("hybrid_sparse_map: {}", hybrid_sparse_map.len());
+    println!("num_dense_locales: {} ({} B)", num_dense_locales, num_dense_locales * dense_row_bit_size / 8);
+
+    let hybrid_sparse_zerotrie: ZeroTrieSimpleAscii<Vec<u8>> =
+        hybrid_sparse_map.iter().map(|(k, v)| (k, *v)).collect();
+    println!("hybrid_sparse_zerotrie: {}", hybrid_sparse_zerotrie.byte_len());
+}
diff --git a/utils/tinystr/Cargo.toml b/utils/tinystr/Cargo.toml
index f633493b4e4..10e66318fba 100644
--- a/utils/tinystr/Cargo.toml
+++ b/utils/tinystr/Cargo.toml
@@ -28,6 +28,7 @@ displaydoc = { workspace = true }
 serde = { workspace = true, features = ["alloc"], optional = true }
 zerovec = { workspace = true, optional = true }
 databake = { workspace = true, optional = true }
+potential_utf = { workspace = true, optional = true }
 
 [dev-dependencies]
 bincode = { workspace = true }
@@ -43,6 +44,7 @@ default = ["alloc"]
 alloc = ["zerovec?/alloc"]
 zerovec = ["dep:zerovec"]
 databake = ["dep:databake"]
+potential_utf = ["dep:potential_utf"]
 serde = ["dep:serde"]
 # No longer does anything
 std = []
diff --git a/utils/tinystr/src/unvalidated.rs b/utils/tinystr/src/unvalidated.rs
index 3758b64ff57..6b176545d35 100644
--- a/utils/tinystr/src/unvalidated.rs
+++ b/utils/tinystr/src/unvalidated.rs
@@ -38,6 +38,12 @@ impl<const N: usize> UnvalidatedTinyAsciiStr<N> {
     pub const fn from_utf8_unchecked(bytes: [u8; N]) -> Self {
         Self(bytes)
     }
+
+    #[cfg(feature = "potential_utf")]
+    #[inline]
+    pub const fn as_potential_utf8(&self) -> &potential_utf::PotentialUtf8 {
+        potential_utf::PotentialUtf8::from_bytes(&self.0)
+    }
 }
 
 impl<const N: usize> TinyAsciiStr<N> {
diff --git a/utils/writeable/src/impls.rs b/utils/writeable/src/impls.rs
index 12f6d6d5dbb..a4d57ebc5bd 100644
--- a/utils/writeable/src/impls.rs
+++ b/utils/writeable/src/impls.rs
@@ -264,3 +264,39 @@ fn test_string_impls() {
     let arr: &[&String] = &[&String::new(), &"abc".to_owned()];
     check_writeable_slice(arr);
 }
+
+macro_rules! impl_write_tuple {
+    ($($index:tt $ty:ident),+) => {
+        impl<$($ty),+> $crate::Writeable for ($($ty),+) where $($ty: $crate::Writeable),+ {
+            #[inline]
+            fn write_to<W: fmt::Write + ?Sized>(&self, sink: &mut W) -> fmt::Result {
+                $(
+                    <$ty as $crate::Writeable>::write_to(&self.$index, sink)?;
+                )+
+                Ok(())
+            }
+            #[inline]
+            fn write_to_parts<W: PartsWrite + ?Sized>(&self, sink: &mut W) -> fmt::Result {
+                $(
+                    <$ty as $crate::Writeable>::write_to_parts(&self.$index, sink)?;
+                )+
+                Ok(())
+            }
+            #[inline]
+            fn writeable_length_hint(&self) -> LengthHint {
+                let mut sum = LengthHint::exact(0);
+                $(
+                    sum += <$ty as $crate::Writeable>::writeable_length_hint(&self.$index);
+                )+
+                sum
+            }
+        }
+    };
+}
+
+impl_write_tuple!(0 A, 1 B);
+impl_write_tuple!(0 A, 1 B, 2 C);
+impl_write_tuple!(0 A, 1 B, 2 C, 3 D);
+impl_write_tuple!(0 A, 1 B, 2 C, 3 D, 4 E);
+impl_write_tuple!(0 A, 1 B, 2 C, 3 D, 4 E, 5 F);
+impl_write_tuple!(0 A, 1 B, 2 C, 3 D, 4 E, 5 F, 6 G);
diff --git a/utils/zerotrie/tests/dense_test.rs b/utils/zerotrie/tests/dense_test.rs
new file mode 100644
index 00000000000..7637f6d61aa
--- /dev/null
+++ b/utils/zerotrie/tests/dense_test.rs
@@ -0,0 +1,55 @@
+// This file is part of ICU4X. For terms of use, please see the file
+// called LICENSE at the top level of the ICU4X source tree
+// (online at: https://github.com/unicode-org/icu4x/blob/main/LICENSE ).
+
+use zerotrie::ZeroTrieSimpleAscii;
+use zerovec::VarZeroVec;
+
+fn s2t<'a>(strings: impl Iterator<Item = &'a str>) -> impl Iterator<Item = (&'a str, usize)> {
+    strings.enumerate().map(|(i, s)| (s, i))
+}
+
+#[test]
+fn test_issue_sizes() {
+    static KEYS: &[&str] = &[
+        "ar/FR", "ar/IR", "ar/SA", "ar/UK", "ar/US", "en/AU", "en/FR", "en/UK", "en/US", "fr/FR",
+        "fr/SA", "fr/UK", "fr/US", "it/IT",
+    ];
+
+    let sparse_zerotrie = ZeroTrieSimpleAscii::from_iter(s2t(KEYS.iter().copied()));
+    assert_eq!(sparse_zerotrie.byte_len(), 71);
+
+    let sparse_vzv = VarZeroVec::<str>::from(KEYS);
+    assert_eq!(sparse_vzv.as_bytes().len(), 98);
+
+    static DENSE_LANGS: &[&str] = &["ar", "en", "fr"];
+    static DENSE_REGIONS: &[&str] = &["FR", "SA", "UK", "US"];
+
+    let dense_lang_zerotrie = ZeroTrieSimpleAscii::from_iter(s2t(DENSE_LANGS.iter().copied()));
+    assert_eq!(dense_lang_zerotrie.byte_len(), 12);
+
+    let dense_region_zerotrie = ZeroTrieSimpleAscii::from_iter(s2t(DENSE_REGIONS.iter().copied()));
+    assert_eq!(dense_region_zerotrie.byte_len(), 16);
+
+    let hybrid_keys = KEYS
+        .iter()
+        .filter(|key| {
+            for lang in DENSE_LANGS.iter() {
+                for region in DENSE_REGIONS.iter() {
+                    if writeable::cmp_str(&(lang, '/', region), key).is_eq() {
+                        return false;
+                    }
+                }
+            }
+            true
+        })
+        .collect::<Vec<_>>();
+    assert_eq!(hybrid_keys.len(), 3);
+
+    let hybrid_zerotrie = ZeroTrieSimpleAscii::from_iter(s2t(hybrid_keys
+        .iter()
+        .copied()
+        .chain(DENSE_LANGS.iter())
+        .copied()));
+    assert_eq!(hybrid_zerotrie.byte_len(), 27);
+}