diff --git a/examples/lang/i18n/data/i18n_items.lres b/examples/lang/i18n/data/i18n_items.lres
new file mode 100644
index 00000000..9ff2f8e1
--- /dev/null
+++ b/examples/lang/i18n/data/i18n_items.lres
@@ -0,0 +1,3 @@
+# i18n.ludic's items: a @Text name is a Key, derived when the row gives none (items.rope.name)
+rope { weight: 0.4 }
+lamp { name: k"items.lamp.name", weight: 1.2 }
diff --git a/examples/lang/i18n/i18n.ludic b/examples/lang/i18n/i18n.ludic
new file mode 100644
index 00000000..342517c9
--- /dev/null
+++ b/examples/lang/i18n/i18n.ludic
@@ -0,0 +1,41 @@
+# i18n.ludic — keys, not English (LANGUAGE.md, "Text keys"). A text the player reads is named by a
+# key, k"pause.resume", of the builtin type Key: not a string, and no string is one. Its English is
+# lang/en.po (package.ludic says `lang "lang" en`), and the compiler checks every key against it. A
+# registry's @Text Key field a row leaves out is filled with its derived key - <registry>.<row>.<field>,
+# or the registry's @TextKey prefix. At run time a Key is its text after a marker byte (1, or 2 for a
+# plural kn"..."), so ludic.i18n's tr() is a cast; here tr, trf and trn are stand-ins that show the key.
+#
+# Running it prints:  pause.resume yes no 13 12 hud.day(3) catch.count[2](trout) items.rope.name items.lamp.name steps.gather_wood.hint
+program I18n {
+  property Item {
+    key: string = ""
+    @Text name: Key = null
+    weight: float = 0.0
+  }
+  registry Items of Item as IT from "data/i18n_items.lres"
+  property StepKind {
+    key: string = ""
+    @Text hint: Key = null
+  }
+  @TextKey("steps") registry StepKinds of StepKind as SK
+  def StepKinds gather_wood { }
+  # ludic.i18n's three, stood in for: the key's text without its marker
+  function tr(key: Key) -> string {
+    let s = string(key)
+    return s[1..len(s)]
+  }
+  function trf(key: Key, a: string) -> string { return `{tr(key)}({a})` }
+  function trn(key: Key, n: int, a: string) -> string { return `{tr(key)}[{n}]({a})` }
+  function yn(b: bool) -> string {
+    if b { return "yes" }
+    return "no"
+  }
+  entry {
+    let resume = k"pause.resume"
+    let same = resume == k"pause.resume"
+    let other = resume == k"pause.close"
+    var out = `{tr(resume)} {yn(same)} {yn(other)} {len(string(resume))} {len(string(kn"catch.count"))} {trf(k"hud.day", "3")}`
+    out = out + ` {trn(kn"catch.count", 2, "trout")} {tr(Items[IT_ROPE].name)} {tr(Items[IT_LAMP].name)} {tr(StepKinds[SK_GATHER_WOOD].hint)}`
+    print(out)
+  }
+}
diff --git a/examples/lang/i18n/i18n_ui.ludic b/examples/lang/i18n/i18n_ui.ludic
new file mode 100644
index 00000000..75b83950
--- /dev/null
+++ b/examples/lang/i18n/i18n_ui.ludic
@@ -0,0 +1,9 @@
+# i18n_ui.ludic — a component's template against lang/en.po: every t('key', ...) in a {hole} names
+# a key en.po has, and gives as many values as its English has holes. Words a player would read that
+# are not a key are "English left" (a warning, counted by ludic deps as english_left) - here the
+# "Paused" line; an element with translate="no" is left alone. `ludicc --check` reports both.
+import "ludic.ui"
+program I18nUi {
+  import "parts/Pause.ludic"
+  entry { print(1) }
+}
diff --git a/examples/lang/i18n/lang/en.po b/examples/lang/i18n/lang/en.po
new file mode 100644
index 00000000..dafcfdc4
--- /dev/null
+++ b/examples/lang/i18n/lang/en.po
@@ -0,0 +1,40 @@
+# The example's source language: the English of every key i18n.ludic and i18n_ui.ludic use.
+msgid ""
+msgstr ""
+"Content-Type: text/plain; charset=UTF-8\n"
+"Plural-Forms: nplurals=2; plural=(n != 1);\n"
+
+#. On the pause menu: returns to play.
+msgid "pause.resume"
+msgstr "Resume"
+
+#. On the pause menu: closes the menu and returns to play.
+msgid "pause.close"
+msgstr "Close"
+
+#. On the map screen: closes the map.
+msgid "map.close"
+msgstr "Close"
+
+#. The day on the HUD. {1} = the day number
+msgid "hud.day"
+msgstr "Day {1}"
+
+#. A catch, counted. {1} = how many, {2} = the species
+msgid "catch.count"
+msgid_plural "catch.count"
+msgstr[0] "{1} {2} caught"
+msgstr[1] "{1} {2} "
+"caught"
+
+#. An item's name: a coil of rope.
+msgid "items.rope.name"
+msgstr "Rope"
+
+#. An item's name: a brass lamp.
+msgid "items.lamp.name"
+msgstr "Lamp"
+
+#. What a chapter step says to do: gather firewood.
+msgid "steps.gather_wood.hint"
+msgstr "Gather wood"
diff --git a/examples/lang/i18n/lang/tr.po b/examples/lang/i18n/lang/tr.po
new file mode 100644
index 00000000..87c13b09
--- /dev/null
+++ b/examples/lang/i18n/lang/tr.po
@@ -0,0 +1,32 @@
+# Turkish: one key missing (hud.day), one fuzzy (pause.close) and one en.po does not have (old.title)
+msgid ""
+msgstr ""
+"Content-Type: text/plain; charset=UTF-8\n"
+"Plural-Forms: nplurals=2; plural=(n != 1);\n"
+
+msgid "pause.resume"
+msgstr "Devam et"
+
+#, fuzzy
+msgid "pause.close"
+msgstr "Kapat"
+
+msgid "map.close"
+msgstr "Kapat"
+
+msgid "catch.count"
+msgid_plural "catch.count"
+msgstr[0] "{1} {2} tutuldu"
+msgstr[1] "{1} {2} tutuldu"
+
+msgid "items.rope.name"
+msgstr "Halat"
+
+msgid "items.lamp.name"
+msgstr "Fener"
+
+msgid "steps.gather_wood.hint"
+msgstr "Odun topla"
+
+msgid "old.title"
+msgstr "Eski"
diff --git a/examples/lang/i18n/package.ludic b/examples/lang/i18n/package.ludic
new file mode 100644
index 00000000..716176a3
--- /dev/null
+++ b/examples/lang/i18n/package.ludic
@@ -0,0 +1,3 @@
+# the key-based text example (i18n.ludic, i18n_ui.ludic): its languages are lang/<code>.po, and
+# lang/en.po is the source every key is checked against
+lang "lang" en
diff --git a/examples/lang/i18n/parts/Pause.ludic b/examples/lang/i18n/parts/Pause.ludic
new file mode 100644
index 00000000..a98eb90b
--- /dev/null
+++ b/examples/lang/i18n/parts/Pause.ludic
@@ -0,0 +1,7 @@
+# Pause.ludic - i18n_ui.ludic's component: its text is keys (Pause.xml), one of them a field the
+# template reads - a Key reaches a template as its marked text, for t(expr)
+component Pause {
+  prop day: int = 1
+  prop caught: int = 0
+  back: Key = k"pause.close"
+}
diff --git a/examples/lang/i18n/parts/Pause.xml b/examples/lang/i18n/parts/Pause.xml
new file mode 100644
index 00000000..8f143d00
--- /dev/null
+++ b/examples/lang/i18n/parts/Pause.xml
@@ -0,0 +1,8 @@
+<div class="pause">
+  <p>{t('pause.resume')}</p>
+  <button title="{t('pause.close')}">{t('hud.day', day)}</button>
+  <button>{t(back)}</button>
+  <p>{t('catch.count', caught, 'trout')}</p>
+  <p translate="no">Maroon Lake 0.5 <b>beta</b></p>
+  <p>Paused</p>
+</div>
diff --git a/examples/rejected/i18n_keys/data_missing.ludic b/examples/rejected/i18n_keys/data_missing.ludic
new file mode 100644
index 00000000..1f139896
--- /dev/null
+++ b/examples/rejected/i18n_keys/data_missing.ludic
@@ -0,0 +1,12 @@
+# phase 26: a @Text Key field a row leaves out takes its derived key (things.axe.name), and en.po must
+# have it; a @Text string field still holding English is a warning, counted as english_left
+program DataMissing {
+  property Thing {
+    key: string = ""
+    @Text name: Key = null
+    @Text blurb: string = ""
+  }
+  registry Things of Thing as TH
+  def Things axe { blurb: "A sharp axe" }
+  entry { print(TH_COUNT) }
+}
diff --git a/examples/rejected/i18n_keys/key_missing.ludic b/examples/rejected/i18n_keys/key_missing.ludic
new file mode 100644
index 00000000..6ee65b79
--- /dev/null
+++ b/examples/rejected/i18n_keys/key_missing.ludic
@@ -0,0 +1,11 @@
+# phase 26: a key literal en.po does not have is refused, and so is a plural key (kn"...") whose
+# en.po entry has no msgid_plural; trf given more values than the English has holes is a warning
+program KeyMissing {
+  function tr(key: Key) -> string { return string(key) }
+  function trf(key: Key, a: string, b: string) -> string { return string(key) + a + b }
+  entry {
+    print(tr(k"pause.gone"))
+    print(tr(kn"pause.resume"))
+    print(trf(k"hud.day", "1", "2"))
+  }
+}
diff --git a/examples/rejected/i18n_keys/key_mixup.ludic b/examples/rejected/i18n_keys/key_mixup.ludic
new file mode 100644
index 00000000..41183557
--- /dev/null
+++ b/examples/rejected/i18n_keys/key_mixup.ludic
@@ -0,0 +1,11 @@
+# phase 26: a Key is not a string and a string is not a Key - text is made from a key, and a key is
+# written k"..."; nor does a key join text with +
+program KeyMixup {
+  function show(s: string) -> void { print(s) }
+  function name_of(k: Key) -> Key { return k }
+  entry {
+    show(k"pause.resume")
+    let k2 = name_of("Resume")
+    print(k2 + "!")
+  }
+}
diff --git a/examples/rejected/i18n_keys/lang/en.po b/examples/rejected/i18n_keys/lang/en.po
new file mode 100644
index 00000000..5f659d55
--- /dev/null
+++ b/examples/rejected/i18n_keys/lang/en.po
@@ -0,0 +1,18 @@
+# The source language of the refused examples: two keys, and one English under two undescribed keys.
+msgid ""
+msgstr ""
+"Content-Type: text/plain; charset=UTF-8\n"
+
+#. On the pause menu: returns to play.
+msgid "pause.resume"
+msgstr "Resume"
+
+#. The day on the HUD. {1} = the day number
+msgid "hud.day"
+msgstr "Day {1}"
+
+msgid "shop.close"
+msgstr "Close"
+
+msgid "map.close"
+msgstr "Close"
diff --git a/examples/rejected/i18n_keys/package.ludic b/examples/rejected/i18n_keys/package.ludic
new file mode 100644
index 00000000..e2404959
--- /dev/null
+++ b/examples/rejected/i18n_keys/package.ludic
@@ -0,0 +1,2 @@
+# the key checks' refusals (key_missing, t_missing, key_mixup, data_missing): lang/en.po is the source
+lang "lang" en
diff --git a/examples/rejected/i18n_keys/parts/Menu.ludic b/examples/rejected/i18n_keys/parts/Menu.ludic
new file mode 100644
index 00000000..ce6260a7
--- /dev/null
+++ b/examples/rejected/i18n_keys/parts/Menu.ludic
@@ -0,0 +1,4 @@
+# Menu.ludic - t_missing.ludic's component: one key en.po lacks
+component Menu {
+  prop day: int = 1
+}
diff --git a/examples/rejected/i18n_keys/parts/Menu.xml b/examples/rejected/i18n_keys/parts/Menu.xml
new file mode 100644
index 00000000..9dc527a4
--- /dev/null
+++ b/examples/rejected/i18n_keys/parts/Menu.xml
@@ -0,0 +1,5 @@
+<div class="menu">
+  <p>{t('pause.resume')}</p>
+  <p>{t('menu.gone')}</p>
+  <p>{t('hud.day')}</p>
+</div>
diff --git a/examples/rejected/i18n_keys/t_missing.ludic b/examples/rejected/i18n_keys/t_missing.ludic
new file mode 100644
index 00000000..29f3097d
--- /dev/null
+++ b/examples/rejected/i18n_keys/t_missing.ludic
@@ -0,0 +1,7 @@
+# phase 26: a template's t('key') is checked against en.po like a key literal - refused when en.po lacks
+# it; t('hud.day') with no value for its {1} is a warning
+import "ludic.ui"
+program TMissing {
+  import "parts/Menu.ludic"
+  entry { print(1) }
+}
diff --git a/tools/ludic-cli/test.ludic b/tools/ludic-cli/test.ludic
index 9c3e41b4..294516e2 100644
--- a/tools/ludic-cli/test.ludic
+++ b/tools/ludic-cli/test.ludic
@@ -74,6 +74,18 @@ function permap_check_case() -> void {
   if not s_contains(capture(`cat {js}`), "the unit is spelled") or not s_contains(capture(`cat {js}`), "deg") { bad2(lbl, capture_line(`head -3 {js}`));  return }
   ok(lbl)
 }
+# phase 26: a template checks clean against en.po, its one line of words a warning, and ludic deps
+# counts it as english_left
+function i18n_check_case() -> void {
+  let lbl = "--check: a component's template against en.po - clean, \"Paused\" English left (a warning), english_left 1 in ludic deps"
+  let js = `{tmp_dir()}/dj_i18n.json`
+  if not shq(`bin/ludicc examples/lang/i18n/i18n_ui.ludic --check --diagnostics=json > {js} 2>/dev/null`) { bad2(lbl, capture_line(`head -3 {js}`));  return }
+  let got = capture(`cat {js}`)
+  if not s_contains(got, "English left: a template's words") or not s_contains(got, "Paused") { bad2(lbl, capture_line(`head -3 {js}`));  return }
+  let dp = capture(`bin/ludic deps examples/lang/i18n/i18n_ui.ludic 2>&1`)
+  if not s_contains(dp, "english_left: 1") { bad2(lbl, `ludic deps said [{s_trim(dp)}]`);  return }
+  ok(lbl)
+}
 # --check --diagnostics=json: refused, with exactly `n` ERRORS on stdout (warnings beside them are not
 # counted), one of the diagnostics holding `want`
 function diag_json_case(path: pointer, n: int, want: pointer, label: pointer) -> void {
@@ -1284,6 +1296,24 @@ function cmd_dev_test() -> int {
   diag_json_case("rejected/permap_maps/permap_maps", 6, "there is no Spots row nowhere in this map", "--check reads every map: a cross-row @Ref names a row of the same map")
   diag_json_case("rejected/permap_maps/permap_maps", 6, "the key t1 is also written at", "--check reads every map: a chunked table's key is unique across the map's chunk files, both places named")
   diag_json_case("rejected/permap_maps/permap_maps", 6, "this map has no examples/rejected/permap_maps/maps/m1/blades.png", "--check reads every map: a game-wide row's @Asset(..., map) file is in each map's directory, unless optional")
+  # phase 26: text keys - k"..." / kn"..." of type Key, checked against package.ludic's lang en.po
+  feat_case("lang/i18n/i18n", "", "pause.resume yes no 13 12 hud.day(3) catch.count[2](trout) items.rope.name items.lamp.name steps.gather_wood.hint", "i18n.ludic (phase 26: k\"...\" and kn\"...\" of type Key, their marker byte, == on keys, a @Text Key field filled with its derived key, @TextKey's prefix)")
+  i18n_check_case()
+  schema_case("lang/i18n/i18n", "{\"key\": \"items.rope.name\", \"kind\": \"data\", \"kinds\": [\"data\"], \"sites\": [\"examples/lang/i18n/data/i18n_items.lres:2:1\"], \"in_source\": true, \"english\": \"Rope\"", "--emit-schema: lang.keys - a derived key, its kind, its site and en.po's English")
+  schema_case("lang/i18n/i18n", "\"unused\": [\"map.close\"]", "--emit-schema: lang.unused - en.po's keys the program uses nowhere")
+  schema_case("lang/i18n/i18n", "\"missing\": [\"hud.day\"], \"fuzzy\": [\"pause.close\"], \"extra\": [\"old.title\"]", "--emit-schema: lang.languages - another .po's missing, fuzzy and extra keys against en.po")
+  schema_case("lang/i18n/i18n", "{\"english\": \"Close\", \"keys\": [\"map.close\", \"pause.close\"]}", "--emit-schema: lang.split - one English under several keys")
+  diag_json_case("rejected/i18n_keys/key_missing", 2, "the key pause.gone is not in examples/rejected/i18n_keys/lang/en.po", "a key literal en.po does not have is refused, at its line and column")
+  diag_json_case("rejected/i18n_keys/key_missing", 2, "is a plural key, and examples/rejected/i18n_keys/lang/en.po:7 gives pause.resume no msgid_plural", "kn\"...\" is a plural key: en.po's entry has a msgid_plural")
+  diag_json_case("rejected/i18n_keys/key_missing", 2, "trf: hud.day is given 2 value(s), and its English in examples/rejected/i18n_keys/lang/en.po has 1 hole(s)", "trf given more values than the key's English has holes: a warning")
+  diag_json_case("rejected/i18n_keys/key_missing", 2, "shop.close has no #. description, and its English", "one English split into several keys wants a #. description on each: a warning at en.po's line")
+  diag_json_case("rejected/i18n_keys/key_mixup", 3, "argument 1 of show wants a string and this is a Key", "a Key is not a string")
+  diag_json_case("rejected/i18n_keys/key_mixup", 3, "argument 1 of name_of wants a Key and this is a string", "a string is not a Key")
+  diag_json_case("rejected/i18n_keys/key_mixup", 3, "+ on a Key", "a Key joins no text")
+  diag_json_case("rejected/i18n_keys/data_missing", 1, "things.axe.name (the derived key of a @Text field the row gives no value): the key things.axe.name is not in", "a @Text Key field a row leaves out: its derived key must be in en.po")
+  diag_json_case("rejected/i18n_keys/data_missing", 1, "English left: things.axe.blurb is", "a @Text string field still holding English: a warning")
+  diag_json_case("rejected/i18n_keys/t_missing", 1, "t('menu.gone'): the key menu.gone is not in", "a template's t('key') is checked against en.po")
+  diag_json_case("rejected/i18n_keys/t_missing", 1, "t(): hud.day is given 0 value(s)", "a template's t('key') given fewer values than the English has holes: a warning")
   feat_case("lang/defaults", "", "a 300.0 8.0 / b 120.0 8.0 / c! 300.0 8.0 / d 300.0 2.0 / x / y", "defaults.ludic (L11: default parameters, positional then named arguments, in a generic too)")
   reject_case("rejected/default_missing", "this call to f leaves out a, which has no default", "a call leaves out only what has a default")
   reject_case("rejected/default_unknown", "f has no parameter c", "a named argument names a parameter the function has")