diff --git a/docs/admin-guide.md b/docs/admin-guide.md
index d8d91e64..e3492e3e 100644
--- a/docs/admin-guide.md
+++ b/docs/admin-guide.md
@@ -180,15 +180,16 @@ What it does, in order:
 1. **Checks Homebrew.** If missing, prints the install one-liner and waits.
 2. **Checks Docker.** If missing, offers to install OrbStack via Homebrew. If installed but not running, asks you to start it and waits.
 3. **Asks for a family name.** Becomes your Matrix server identity. Permanent. Pick something short and lowercase-friendly. `mueller` is fine; "The Müller-Schmidt Family" gets sanitized to `mueller-schmidt`.
-4. **Asks for your first name.** Becomes the admin account on every stacklet. Default password is your first name in lowercase. Change it at first login.
-5. **Asks for additional family members.** Empty input ends the loop. Each member gets their own account on each stacklet.
-6. **Writes config.** Three files appear:
+4. **Asks for your family's language.** `en` or `de`, proposed from the Mac's time zone. The bots answer in it, documents are tagged in it, and voice messages are transcribed in it. Choose it deliberately: changing it later leaves the first set of document tags behind.
+5. **Asks for your first name.** Becomes the admin account on every stacklet. Default password is your first name in lowercase. Change it at first login.
+6. **Asks for additional family members.** Empty input ends the loop. Each member gets their own account on each stacklet.
+7. **Writes config.** Three files appear:
    - `stack.toml`: central config, gitignored, yours to edit.
    - `users.toml`: family roster, gitignored.
    - `.stack/secrets.toml`: auto-generated passwords for service accounts. Treat like a password manager export.
-7. **Brings up `messages` and `core`.** Pulls Synapse, Element and Postgres images (about 600 MB), starts them, creates Matrix accounts, seeds two default rooms (`#famchat`, `#famstack`).
-8. **Installs the `famstack` command.** A small script in Homebrew's `bin` directory that runs this checkout's `./stack`, so `famstack status` works from any directory. If another command called `famstack` is already on your PATH, the installer leaves it alone and the final screen says `./stack` instead.
-9. **Prints a sign-in URL.** Something like `http://192.168.1.42:42030`.
+8. **Brings up `messages` and `core`.** Pulls Synapse, Element and Postgres images (about 600 MB), starts them, creates Matrix accounts, seeds two default rooms (`#famchat`, `#famstack`).
+9. **Installs the `famstack` command.** A small script in Homebrew's `bin` directory that runs this checkout's `./stack`, so `famstack status` works from any directory. If another command called `famstack` is already on your PATH, the installer leaves it alone and the final screen says `./stack` instead.
+10. **Prints a sign-in URL.** Something like `http://192.168.1.42:42030`.
 
 Total time on a fresh Mac with a decent connection: 5 to 10 minutes.
 
@@ -588,7 +589,7 @@ schedule = "0 0 3 * * *"         # Watchtower nightly image updates
 
 [ai]
 default = "mlx-community/Qwen3.5-9B-MLX-4bit"   # change to match your RAM
-language = "en"                                   # "de" for German voice/transcription
+language = "en"                                   # the voice that reads answers aloud; can differ from [core]
 
 [memory]
 wiki_auto_rebuild = true         # curator refreshes member pages after filings
@@ -602,7 +603,7 @@ Key things to know:
 - **dns_provider**: with a domain, `"hetzner"` or `"cloudflare"` serves everything over HTTPS, with certificates Caddy obtains through the provider's API. Empty serves plain HTTP. The API token is stored with `./stack infra dns-token`, never in `stack.toml`.
 - **host**: the hostname used in port-mode URLs and hints. Empty = auto-detect the LAN IP (right for households: phones need it). Set to `localhost` for a single-machine setup, or to a fixed name like `mac-mini.local` if the LAN IP keeps shifting.
 - **data_dir**: where all persistent data lives. Back this up. Outside the git repo.
-- **language**: detected from your timezone. Controls which document categories get seeded (German or English). Change it and run `./stack restart docs` to seed missing tags.
+- **language**: asked during install, proposed from your timezone. `[core] language` is the family's language: the bots answer in it, document categories are seeded in it, voice messages are transcribed in it. Changing it later seeds the other set of tags alongside the first with `./stack restart docs`; the first set stays. `[ai] language` is the language the stack speaks to you, the voice that reads answers aloud. The installer sets it to the family language; set it to `en` for an English voice in a German household. `stack doctor` warns when `[core] language` is missing, which only happens on installs from before the installer wrote it.
 - **AI model**: installer picks one for your RAM tier. Alternatives are listed as comments in `stack.toml`. Switch by uncommenting a different line and running `./stack setup ai`.
 
 ### users.toml
diff --git a/lib/stack/cli.py b/lib/stack/cli.py
index 0dd98aa8..d3380840 100644
--- a/lib/stack/cli.py
+++ b/lib/stack/cli.py
@@ -1114,6 +1114,11 @@ def missing_secrets(stacklet_id):
         running={sid for sid in stacklets if docker.containers_for(sid)},
     )
 
+    language = doctor.check_language(stck._cfg("core", "language", ""),
+                                     stck._cfg("ai", "language", ""))
+    if language:
+        findings.append(language)
+
     # What this instance is running, and whether a release has passed it.
     # No fetch: doctor is run often, and often when something is
     # unreachable, so it answers from the tags this clone already has.
diff --git a/lib/stack/doctor.py b/lib/stack/doctor.py
index 9f1a44ca..3e69d702 100644
--- a/lib/stack/doctor.py
+++ b/lib/stack/doctor.py
@@ -194,6 +194,31 @@ def check_release(position: str, latest: str, up_to_date: bool) -> Finding | Non
     )
 
 
+def check_language(core_language: str, ai_language: str) -> Finding | None:
+    """Whether the family's language, `[core] language`, is set.
+
+    Installs from before the installer wrote it have none. Everything that
+    reads the family language then falls back to `[ai] language`, the
+    language the stack speaks to you, which may be a different one: the
+    bots, the document categories and transcription follow the voice.
+    A `[core] language` different from `[ai] language` is a valid setup
+    and not reported.
+    """
+    if core_language:
+        return None
+    fallback = ai_language or "en"
+    return Finding(
+        level=WARN,
+        title="no family language set",
+        detail=(f"stack.toml has no `language` under [core]. The bots, document "
+                f"tags and transcription fall back to \"{fallback}\""
+                + (", the language of the voice under [ai]." if ai_language else ".")),
+        fix=(f'add language = "{fallback}" under [core] in stack.toml (or the '
+             f"language your family reads), then restart what is running: "
+             f"stack restart <id>..."),
+    )
+
+
 def check_endpoint(name: str, url: str, reachable: bool) -> Finding | None:
     """A configured endpoint that does not answer.
 
diff --git a/lib/stack/installer.py b/lib/stack/installer.py
index de38dd53..0fe6fc97 100644
--- a/lib/stack/installer.py
+++ b/lib/stack/installer.py
@@ -98,6 +98,16 @@ def detect_language(timezone: str) -> str:
     return _TZ_LANGUAGE.get(timezone, "en")
 
 
+LANGUAGES = {"en": "English", "de": "Deutsch"}
+
+
+def validate_language(value: str) -> str | None:
+    """The languages the seeded taxonomy and the bots' texts exist in."""
+    if value in LANGUAGES:
+        return None
+    return "Choose " + " or ".join(LANGUAGES)
+
+
 # (min_ram_gb, model_id, label)
 # Qwen3.6 only shipped a 27B dense and a 35B-A3B MoE — no small variant — so
 # the lightweight tier stays on Qwen3.5-9B (3.6's smallest 4bit is 16 GB of
@@ -297,7 +307,10 @@ def write_stack_toml(family_name, server_name, timezone, language="en"):
 provider = ""
 openai_url = ""
 openai_key = ""
-language = "en"
+# The language the stack speaks to you: the voice that reads answers
+# aloud. Starts as the family language; it can differ. Transcription and
+# document tags follow [core] language.
+language = "{language}"
 {model_block}
 
 [messages]
@@ -372,8 +385,10 @@ def show_existing_config():
         kv("Domain", core["domain"])
     if ai.get("openai_url"):
         kv("AI server", ai["openai_url"])
+    if core.get("language"):
+        kv("Language", core["language"])
     if ai.get("language"):
-        kv("AI language", ai["language"])
+        kv("Voice", ai["language"])
     if messages.get("server_name"):
         kv("Chat server", messages["server_name"])
     nl()
@@ -467,6 +482,20 @@ def wizard():
 
     server_name = sanitize_server_name(family_name)
 
+    # ── Language ───────────────────────────────────────────────────────
+    # Asked, not only guessed: it names the document categories seeded
+    # into Paperless, and changing it later leaves the first set behind.
+
+    timezone = detect_timezone()
+    nl()
+    out("Which language does your family read? The bots answer in it,")
+    out("documents are tagged in it, and voice messages are transcribed in it.")
+    nl()
+    language = ask(f"Language ({', '.join(LANGUAGES)})",
+                   default=detect_language(timezone), validate=validate_language)
+    if not language:
+        return None
+
     # ── Admin ──────────────────────────────────────────────────────────
 
     nl()
@@ -506,6 +535,7 @@ def wizard():
     rule()
     nl()
     bold(f"The {ORANGE}{family_plural(family_name)}{RESET}")
+    dim(f"Language: {LANGUAGES[language]}")
     nl()
     for u in users:
         uid = user_id(u)
@@ -547,9 +577,6 @@ def wizard():
     section("Setting up", "Writing config and starting messages")
     nl()
 
-    timezone = detect_timezone()
-    language = detect_language(timezone)
-
     with Spinner("Writing stack.toml"):
         write_stack_toml(family_name, server_name, timezone, language)
 
diff --git a/stack.example.toml b/stack.example.toml
index 399e32e4..fb55e84f 100644
--- a/stack.example.toml
+++ b/stack.example.toml
@@ -115,8 +115,8 @@ whisper_url = "http://localhost:42062/v1"
 # whisper_key = ""               # only for a speech server that needs one
 # whisper_model = "whisper-1"    # the speech model to ask the server for
 
-# Language for AI interactions — controls TTS voice selection and
-# default Whisper transcription language.
+# The language the stack speaks to you: the voice that reads answers
+# aloud. Can differ from [core] language, which decides transcription.
 # "en" = English (alloy voice), "de" = German (onyx voice)
 language = "en"
 
diff --git a/stacklets/core/stacklet.toml b/stacklets/core/stacklet.toml
index dd21ef8e..333aa2af 100644
--- a/stacklets/core/stacklet.toml
+++ b/stacklets/core/stacklet.toml
@@ -129,10 +129,11 @@ TOOLS_PORT = "42000"
 # midnight is filed under the previous day.
 TIMEZONE         = "{timezone}"
 
-# Household language — drives bot-side i18n, ontology rendering, and
-# any prompt that should be in the family's primary language. Distinct
-# from `[ai].language` (`{ai_language}`), which controls AI subsystem
-# settings like TTS voice and Whisper transcription language.
+# Household language — drives bot-side i18n, ontology rendering, any
+# prompt that should be in the family's primary language, and the
+# language voice messages are transcribed in. Distinct from
+# `[ai].language` (`{ai_language}`), the language the stack speaks to
+# you: it picks the voice that reads answers aloud.
 LANGUAGE         = "{language}"
 AI_DEFAULT_MODEL = "{ai_default_model}"
 AI_MODELS_JSON   = "{ai_models_json}"
diff --git a/tests/e2e/install/test_first_install.py b/tests/e2e/install/test_first_install.py
index 18d833dc..52f59822 100644
--- a/tests/e2e/install/test_first_install.py
+++ b/tests/e2e/install/test_first_install.py
@@ -59,6 +59,7 @@
 def _answers() -> dict[str, list[str]]:
     return {
         "Family name": [FAMILY],
+        "Language (en, de)": ["en"],
         "Your first name": [ADMIN],
         "Name (leave empty to continue)": [*MEMBERS, ""],
         "Ready?": ["y"],
@@ -389,6 +390,13 @@ def test_the_secrets_file_holds_the_service_admin_password(install):
     login(homeserver(printed_url(install)), account[1], secrets["global__ADMIN_PASSWORD"])
 
 
+def test_the_answered_language_is_the_family_language(install):
+    # Answered "en" on a Mac whose time zone proposes "de": the answer wins,
+    # for the family and as the first voice language.
+    cfg = tomllib.loads((Path(CLONE) / "stack.toml").read_text())
+    assert (cfg["core"]["language"], cfg["ai"]["language"]) == ("en", "en")
+
+
 def test_the_printed_commands_name_real_commands(install):
     """Run from the checkout as `./stack`, each printed command parses.
 
diff --git a/tests/unit/framework/test_doctor.py b/tests/unit/framework/test_doctor.py
index 72ea3f83..5d2fd377 100644
--- a/tests/unit/framework/test_doctor.py
+++ b/tests/unit/framework/test_doctor.py
@@ -7,6 +7,7 @@
 from __future__ import annotations
 
 from stack.doctor import (
+    check_language,
     ERROR,
     Finding,
     check_endpoint,
@@ -438,3 +439,24 @@ def test_a_second_provider_is_ignored_and_doctor_says_which(self):
         [found] = check_oidc(["id", "sso"], {}, running={"id"})
         assert found.level == WARN
         assert "id" in found.detail and "sso" in found.detail
+
+
+class TestLanguage:
+    """`[core] language` is the family's language; `[ai] language` the
+    language the stack speaks to you. Early installs have only the second,
+    and everything silently falls back to it. Doctor says so."""
+
+    def test_an_install_without_a_family_language_is_told_to_set_one(self):
+        finding = check_language("", "de")
+
+        assert finding.title == "no family language set"
+        assert 'language = "de"' in finding.fix
+        assert "voice" in finding.detail
+        assert finding.is_error is False
+
+    def test_without_either_it_falls_back_to_english(self):
+        assert 'language = "en"' in check_language("", "").fix
+
+    def test_a_voice_in_another_language_is_a_valid_setup(self):
+        """German documents, an English voice: nothing to report."""
+        assert check_language("de", "en") is None
diff --git a/tests/unit/framework/test_install_language.py b/tests/unit/framework/test_install_language.py
new file mode 100644
index 00000000..b468a492
--- /dev/null
+++ b/tests/unit/framework/test_install_language.py
@@ -0,0 +1,43 @@
+"""The family's language, chosen once in the install wizard.
+
+It names the document categories seeded into Paperless, the language the
+bots answer in and the language voice messages are transcribed in. The
+wizard proposes one from the Mac's time zone and asks; the answer is
+`[core] language`, and also the first value of `[ai] language`, the
+language the stack speaks to you, which can be changed on its own.
+"""
+
+import tomllib
+
+from stack import installer
+
+
+def test_the_proposal_follows_the_time_zone():
+    assert installer.detect_language("Europe/Berlin") == "de"
+    assert installer.detect_language("America/New_York") == "en"
+
+
+def test_only_languages_with_a_seeded_taxonomy_are_accepted():
+    assert installer.validate_language("de") is None
+    assert installer.validate_language("en") is None
+    assert installer.validate_language("fr") == "Choose en or de"
+
+
+def test_the_chosen_language_is_the_family_language_and_the_first_voice(tmp_path, monkeypatch):
+    monkeypatch.setattr(installer, "REPO_ROOT", tmp_path)
+
+    installer.write_stack_toml("Simpson", "simpson", "Europe/Berlin", "de")
+
+    cfg = tomllib.loads((tmp_path / "stack.toml").read_text())
+    assert cfg["core"]["language"] == "de"
+    # The voice starts in the same language and can be changed on its own.
+    assert cfg["ai"]["language"] == "de"
+
+
+def test_an_english_choice_in_a_german_time_zone_is_kept(tmp_path, monkeypatch):
+    monkeypatch.setattr(installer, "REPO_ROOT", tmp_path)
+
+    installer.write_stack_toml("Simpson", "simpson", "Europe/Berlin", "en")
+
+    cfg = tomllib.loads((tmp_path / "stack.toml").read_text())
+    assert cfg["core"]["language"] == "en"