diff --git a/.github/workflows/main.yml b/.github/workflows/main.yml
index fe579267..7a1299f7 100644
--- a/.github/workflows/main.yml
+++ b/.github/workflows/main.yml
@@ -17,9 +17,9 @@ jobs:
       fail-fast: false
       matrix:
         include:
-          - os: ubuntu-22.04
-            erlang: "27.2"
-            elixir: "1.18"
+          - os: ubuntu-24.04
+            erlang: "29.0"
+            elixir: "1.20"
             lint: true
             coverage: true
 
@@ -31,7 +31,7 @@ jobs:
       GITHUB_TOKEN: ${{ secrets.GITHUB_TOKEN }}
 
     steps:
-      - uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+      - uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6.0.3
 
       - name: Install OTP and Elixir
         uses: erlef/setup-beam@fc68ffb90438ef2936bbb3251622353b3dcb2f93 # v1.24.0
diff --git a/.github/workflows/publish-to-hex.yml b/.github/workflows/publish-to-hex.yml
index 791f63dd..cc41e269 100644
--- a/.github/workflows/publish-to-hex.yml
+++ b/.github/workflows/publish-to-hex.yml
@@ -16,13 +16,13 @@ jobs:
 
     steps:
       - name: Checkout this repository
-        uses: actions/checkout@de0fac2e4500dabe0009e67214ff5f5447ce83dd # v6.0.2
+        uses: actions/checkout@df4cb1c069e1874edd31b4311f1884172cec0e10 # v6.0.3
 
       - name: Install Erlang and Elixir
         uses: erlef/setup-beam@fc68ffb90438ef2936bbb3251622353b3dcb2f93 # v1.24.0
         with:
-          otp-version: "27.2"
-          elixir-version: "1.18"
+          otp-version: "29.0"
+          elixir-version: "1.20"
 
       - name: Fetch dependencies
         run: mix deps.get
diff --git a/CHANGELOG.md b/CHANGELOG.md
index f7d38080..6cd9c7c4 100644
--- a/CHANGELOG.md
+++ b/CHANGELOG.md
@@ -1,5 +1,9 @@
 # Changelog
 
+## Unreleased
+
+  * Parallelize per-locale merging in `mix gettext.merge`.
+
 ## v1.0.2
 
   * Only skip manifest removal on Elixir v1.19.3+
diff --git a/lib/mix/tasks/gettext.merge.ex b/lib/mix/tasks/gettext.merge.ex
index 49efebc4..3371bbab 100644
--- a/lib/mix/tasks/gettext.merge.ex
+++ b/lib/mix/tasks/gettext.merge.ex
@@ -191,9 +191,17 @@ defmodule Mix.Tasks.Gettext.Merge do
   end
 
   defp merge_all_locale_dirs(pot_dir, opts, gettext_config) do
-    for locale <- File.ls!(pot_dir), File.dir?(Path.join(pot_dir, locale)) do
-      merge_dirs(locale_dir(pot_dir, locale), pot_dir, locale, opts, gettext_config)
-    end
+    pot_dir
+    |> File.ls!()
+    |> Enum.filter(&File.dir?(Path.join(pot_dir, &1)))
+    |> Task.async_stream(
+      fn locale ->
+        merge_dirs(locale_dir(pot_dir, locale), pot_dir, locale, opts, gettext_config)
+      end,
+      ordered: false,
+      timeout: :infinity
+    )
+    |> Stream.run()
   end
 
   def locale_dir(pot_dir, locale) do
diff --git a/mix.lock b/mix.lock
index 84b78a81..7e7415a3 100644
--- a/mix.lock
+++ b/mix.lock
@@ -1,10 +1,10 @@
 %{
-  "castore": {:hex, :castore, "1.0.10", "43bbeeac820f16c89f79721af1b3e092399b3a1ecc8df1a472738fd853574911", [:mix], [], "hexpm", "1b0b7ea14d889d9ea21202c43a4fa015eb913021cb535e8ed91946f4b77a8848"},
+  "castore": {:hex, :castore, "1.0.19", "6903cabdfd9d1af46454126e7c8385186659dd33ecfb74a885cae52221ad6109", [:mix], [], "hexpm", "3669e6cab13f54c2df26b3e6833745d647f35b6e30d8ddd5975df0d5c842ca98"},
   "earmark_parser": {:hex, :earmark_parser, "1.4.44", "f20830dd6b5c77afe2b063777ddbbff09f9759396500cdbe7523efd58d7a339c", [:mix], [], "hexpm", "4778ac752b4701a5599215f7030989c989ffdc4f6df457c5f36938cc2d2a2750"},
   "ex_doc": {:hex, :ex_doc, "0.40.3", "4a972ffe64bc07dc605af487e98fc19b72a4185f55ca031b94c0552d6071c1d9", [:mix], [{:earmark_parser, "~> 1.4.44", [hex: :earmark_parser, repo: "hexpm", optional: false]}, {:makeup_c, ">= 0.1.0", [hex: :makeup_c, repo: "hexpm", optional: true]}, {:makeup_elixir, "~> 0.14 or ~> 1.0", [hex: :makeup_elixir, repo: "hexpm", optional: false]}, {:makeup_erlang, "~> 0.1 or ~> 1.0", [hex: :makeup_erlang, repo: "hexpm", optional: false]}, {:makeup_html, ">= 0.1.0", [hex: :makeup_html, repo: "hexpm", optional: true]}], "hexpm", "2756e357742fecd9749b489b85d67c9ce99c465f2e75728d9e6dc8d704b973de"},
-  "excoveralls": {:hex, :excoveralls, "0.18.3", "bca47a24d69a3179951f51f1db6d3ed63bca9017f476fe520eb78602d45f7756", [:mix], [{:castore, "~> 1.0", [hex: :castore, repo: "hexpm", optional: true]}, {:jason, "~> 1.0", [hex: :jason, repo: "hexpm", optional: false]}], "hexpm", "746f404fcd09d5029f1b211739afb8fb8575d775b21f6a3908e7ce3e640724c6"},
+  "excoveralls": {:hex, :excoveralls, "0.18.5", "e229d0a65982613332ec30f07940038fe451a2e5b29bce2a5022165f0c9b157e", [:mix], [{:castore, "~> 1.0", [hex: :castore, repo: "hexpm", optional: true]}, {:jason, "~> 1.0", [hex: :jason, repo: "hexpm", optional: false]}], "hexpm", "523fe8a15603f86d64852aab2abe8ddbd78e68579c8525ae765facc5eae01562"},
   "expo": {:hex, :expo, "1.1.1", "4202e1d2ca6e2b3b63e02f69cfe0a404f77702b041d02b58597c00992b601db5", [:mix], [], "hexpm", "5fb308b9cb359ae200b7e23d37c76978673aa1b06e2b3075d814ce12c5811640"},
-  "jason": {:hex, :jason, "1.4.4", "b9226785a9aa77b6857ca22832cffa5d5011a667207eb2a0ad56adb5db443b8a", [:mix], [{:decimal, "~> 1.0 or ~> 2.0", [hex: :decimal, repo: "hexpm", optional: true]}], "hexpm", "c5eb0cab91f094599f94d55bc63409236a8ec69a21a67814529e8d5f6cc90b3b"},
+  "jason": {:hex, :jason, "1.4.5", "2e3a008590b0b8d7388c20293e9dcc9cf3e5d642fd2a114e4cbbb52e595d940a", [:mix], [{:decimal, "~> 1.0 or ~> 2.0 or ~> 3.0", [hex: :decimal, repo: "hexpm", optional: true]}], "hexpm", "b0c823996102bcd0239b3c2444eb00409b72f6a140c1950bc8b457d836b30684"},
   "makeup": {:hex, :makeup, "1.2.1", "e90ac1c65589ef354378def3ba19d401e739ee7ee06fb47f94c687016e3713d1", [:mix], [{:nimble_parsec, "~> 1.4", [hex: :nimble_parsec, repo: "hexpm", optional: false]}], "hexpm", "d36484867b0bae0fea568d10131197a4c2e47056a6fbe84922bf6ba71c8d17ce"},
   "makeup_elixir": {:hex, :makeup_elixir, "1.0.1", "e928a4f984e795e41e3abd27bfc09f51db16ab8ba1aebdba2b3a575437efafc2", [:mix], [{:makeup, "~> 1.0", [hex: :makeup, repo: "hexpm", optional: false]}, {:nimble_parsec, "~> 1.2.3 or ~> 1.3", [hex: :nimble_parsec, repo: "hexpm", optional: false]}], "hexpm", "7284900d412a3e5cfd97fdaed4f5ed389b8f2b4cb49efc0eb3bd10e2febf9507"},
   "makeup_erlang": {:hex, :makeup_erlang, "1.1.0", "835f7e60792e08824cda445639555d7bf1bbbddb1b60b306e33cb6f6db24dc74", [:mix], [{:makeup, "~> 1.0", [hex: :makeup, repo: "hexpm", optional: false]}], "hexpm", "1cd6780fb1dd1a03979abaed0fe82712b0625118fd5257d3ebbf73f960c73c3c"},
diff --git a/test/gettext/extractor_test.exs b/test/gettext/extractor_test.exs
index cac32e50..80f45ab6 100644
--- a/test/gettext/extractor_test.exs
+++ b/test/gettext/extractor_test.exs
@@ -461,13 +461,16 @@ defmodule Gettext.ExtractorTest do
     end
     """
 
+    # No trailing newline in the expected string below: the logged message ends
+    # without one, so when color is enabled the reset code (\e[0m) sits between
+    # the message and Logger's newline. Anchoring on "\n" would fail in a TTY.
     assert capture_log(fn ->
              Code.compile_string(code, Path.join(File.cwd!(), "foo.ex"))
            end) =~
              """
              Plural message for 'one error' is not matching:
              Using 'multiple errors' instead of '%{count} errors'.
-             References: foo.ex:9, foo.ex:10
+             References: foo.ex:9, foo.ex:10\
              """
   after
     Extractor.disable()
diff --git a/test/gettext/interpolation/default_test.exs b/test/gettext/interpolation/default_test.exs
index 94ce9109..e2fc766c 100644
--- a/test/gettext/interpolation/default_test.exs
+++ b/test/gettext/interpolation/default_test.exs
@@ -107,8 +107,12 @@ defmodule Gettext.Interpolation.DefaultTest do
         )
       end
 
+      # Building the empty bindings via `Map.drop/2` (rather than a `%{}`
+      # literal) keeps the compiler's type checker from inferring that
+      # `translate` only accepts maps with a `:count` key, which would flag
+      # this intentional missing-key case.
       assert_raise MatchError, fn ->
-        translate.(%{})
+        translate.(Map.drop(%{count: 7}, [:count]))
       end
 
       assert {:ok, "7 shoes"} = translate.(%{count: 7})
diff --git a/test/gettext/merger_test.exs b/test/gettext/merger_test.exs
index 916791be..7db679dd 100644
--- a/test/gettext/merger_test.exs
+++ b/test/gettext/merger_test.exs
@@ -67,8 +67,7 @@ defmodule Gettext.MergerTest do
                   %Message.Singular{msgid: "obs_auto", obsolete: true},
                   %Message.Singular{msgid: "obs_manual", obsolete: true}
                 ]
-              },
-              stats} =
+              }, stats} =
                Merger.merge(
                  old_po,
                  new_pot,
diff --git a/test/mix/tasks/gettext.extract_test.exs b/test/mix/tasks/gettext.extract_test.exs
index 97957c66..8a1c8b71 100644
--- a/test/mix/tasks/gettext.extract_test.exs
+++ b/test/mix/tasks/gettext.extract_test.exs
@@ -14,14 +14,15 @@ defmodule Mix.Tasks.Gettext.ExtractTest do
 
   test "extracting and extracting with --merge", %{test: test, tmp_dir: tmp_dir} = context do
     create_test_mix_file(context)
+    mod = unique_module(test)
 
     write_file(context, "lib/my_app.ex", """
-    defmodule MyApp.Gettext do
+    defmodule #{mod}.Gettext do
       use Gettext.Backend, otp_app: #{inspect(test)}
     end
 
-    defmodule MyApp do
-      use Gettext, backend: MyApp.Gettext
+    defmodule #{mod} do
+      use Gettext, backend: #{mod}.Gettext
       def foo(), do: gettext("hello")
     end
     """)
@@ -43,8 +44,8 @@ defmodule Mix.Tasks.Gettext.ExtractTest do
     # Test --merge too.
 
     write_file(context, "lib/other.ex", """
-    defmodule MyApp.Other do
-      use Gettext, backend: MyApp.Gettext
+    defmodule #{mod}.Other do
+      use Gettext, backend: #{mod}.Gettext
       def foo(), do: dgettext("my_domain", "other")
     end
     """)
@@ -70,21 +71,22 @@ defmodule Mix.Tasks.Gettext.ExtractTest do
   test "--check-up-to-date should fail if no POT files have been created",
        %{test: test, tmp_dir: tmp_dir} = context do
     create_test_mix_file(context)
+    mod = unique_module(test)
 
     write_file(context, "lib/my_app.ex", """
-    defmodule MyApp.Gettext do
+    defmodule #{mod}.Gettext do
       use Gettext.Backend, otp_app: #{inspect(test)}
     end
 
-    defmodule MyApp do
-      use Gettext, backend: MyApp.Gettext
+    defmodule #{mod} do
+      use Gettext, backend: #{mod}.Gettext
       def foo(), do: gettext("hello")
     end
     """)
 
     write_file(context, "lib/other.ex", """
-    defmodule MyApp.Other do
-      use Gettext, backend: MyApp.Gettext
+    defmodule #{mod}.Other do
+      use Gettext, backend: #{mod}.Gettext
       def foo(), do: dgettext("my_domain", "other")
     end
     """)
@@ -109,14 +111,15 @@ defmodule Mix.Tasks.Gettext.ExtractTest do
   test "--check-up-to-date should pass if nothing changed",
        %{test: test, tmp_dir: tmp_dir} = context do
     create_test_mix_file(context, write_reference_comments: false)
+    mod = unique_module(test)
 
     write_file(context, "lib/my_app.ex", """
-    defmodule MyApp.Gettext do
+    defmodule #{mod}.Gettext do
       use Gettext.Backend, otp_app: #{inspect(test)}
     end
 
-    defmodule MyApp do
-      use Gettext, backend: MyApp.Gettext
+    defmodule #{mod} do
+      use Gettext, backend: #{mod}.Gettext
       def foo(), do: gettext("hello")
     end
     """)
@@ -135,21 +138,22 @@ defmodule Mix.Tasks.Gettext.ExtractTest do
   test "--check-up-to-date should fail if POT files are outdated",
        %{test: test, tmp_dir: tmp_dir} = context do
     create_test_mix_file(context)
+    mod = unique_module(test)
 
     write_file(context, "lib/my_app.ex", """
-    defmodule MyApp.Gettext do
+    defmodule #{mod}.Gettext do
       use Gettext.Backend, otp_app: #{inspect(test)}
     end
 
-    defmodule MyApp do
-      use Gettext, backend: MyApp.Gettext
+    defmodule #{mod} do
+      use Gettext, backend: #{mod}.Gettext
       def foo(), do: gettext("hello")
     end
     """)
 
     write_file(context, "lib/other.ex", """
-    defmodule MyApp.Other do
-      use Gettext, backend: MyApp.Gettext
+    defmodule #{mod}.Other do
+      use Gettext, backend: #{mod}.Gettext
       def foo(), do: dgettext("my_domain", "other")
     end
     """)
@@ -159,12 +163,12 @@ defmodule Mix.Tasks.Gettext.ExtractTest do
     end)
 
     write_file(context, "lib/my_app.ex", """
-    defmodule MyApp.Gettext do
+    defmodule #{mod}.Gettext do
       use Gettext.Backend, otp_app: #{inspect(test)}
     end
 
-    defmodule MyApp do
-      use Gettext, backend: MyApp.Gettext
+    defmodule #{mod} do
+      use Gettext, backend: #{mod}.Gettext
       def foo(), do: gettext("hello world")
     end
     """)
diff --git a/test/support/mix_project_helpers.ex b/test/support/mix_project_helpers.ex
index 4e6c427f..7cb11bde 100644
--- a/test/support/mix_project_helpers.ex
+++ b/test/support/mix_project_helpers.ex
@@ -1,4 +1,14 @@
 defmodule GettextTest.MixProjectHelpers do
+  # Returns a module name segment that is unique per test. Tests in this suite
+  # run in the same VM and reuse fixture module names; because
+  # `Mix.Project.in_project/4` is called with `prune_code_paths: false`, every
+  # test's compiled fixtures stay in the code path. Reusing a module name across
+  # tests would let an earlier test's stale beam shadow the freshly compiled one,
+  # so we derive a unique base module name from the test name instead.
+  def unique_module(test) do
+    "MyApp" <> Integer.to_string(:erlang.phash2(test))
+  end
+
   def create_test_mix_file(context, gettext_config \\ []) do
     write_file(context, "mix.exs", """
     defmodule MyApp.MixProject do