diff --git a/game/i18n/texts.csv b/game/i18n/texts.csv
new file mode 100644
index 0000000..6df10eb
--- /dev/null
+++ b/game/i18n/texts.csv
@@ -0,0 +1,10 @@
+keys,de,en
+STONE_COUNT,Stein: %d,Stone: %d
+SAVED,Gespeichert,Saved
+SAVE_FAILED,Speichern fehlgeschlagen,Saving failed
+LOADED,Spielstand geladen,Save loaded
+LOAD_FAILED,Der Spielstand ließ sich nicht laden,The save could not be loaded
+INVENTORY_FULL,Die Tasche ist voll,Your bag is full
+PAUSED,Pause,Paused
+SIMULATION_STOPPED,Die Simulation wurde angehalten,The simulation stopped
+HELP,WASD: laufen · Linke Maustaste: Stein schlagen · F5: speichern · F9: laden · Esc: Pause,WASD: walk · Left mouse button: break rock · F5: save · F9: load · Esc: pause
diff --git a/game/i18n/texts.csv.import b/game/i18n/texts.csv.import
new file mode 100644
index 0000000..8dd0c09
--- /dev/null
+++ b/game/i18n/texts.csv.import
@@ -0,0 +1,3 @@
+[remap]
+
+importer="keep"
diff --git a/game/scripts/i18n.gd b/game/scripts/i18n.gd
new file mode 100644
index 0000000..e032740
--- /dev/null
+++ b/game/scripts/i18n.gd
@@ -0,0 +1,41 @@
+class_name I18n
+extends RefCounted
+## Loads the game's texts from a CSV file: the first column holds the key,
+## every further column one language, named in the first row.
+##
+## The file is read at run time. Its import setting is "keep", so Godot
+## generates no translation files from it.
+
+const TEXTS_FILE := "res://i18n/texts.csv"
+
+static var _installed := false
+
+
+## Adds the translations of TEXTS_FILE to the TranslationServer, once.
+static func install() -> void:
+	if _installed:
+		return
+	for translation in load_translations(TEXTS_FILE):
+		TranslationServer.add_translation(translation)
+	_installed = true
+
+
+## One Translation per language column of the CSV file at `path`.
+static func load_translations(path: String) -> Array[Translation]:
+	var translations: Array[Translation] = []
+	var file := FileAccess.open(path, FileAccess.READ)
+	if file == null:
+		push_error("texts not found: %s" % path)
+		return translations
+	var header := file.get_csv_line()
+	for column in range(1, header.size()):
+		var translation := Translation.new()
+		translation.locale = header[column]
+		translations.append(translation)
+	while not file.eof_reached():
+		var row := file.get_csv_line()
+		if row.size() < header.size() or row[0].is_empty():
+			continue
+		for column in range(1, header.size()):
+			translations[column - 1].add_message(row[0], row[column])
+	return translations
diff --git a/game/scripts/i18n.gd.uid b/game/scripts/i18n.gd.uid
new file mode 100644
index 0000000..ddf548c
--- /dev/null
+++ b/game/scripts/i18n.gd.uid
@@ -0,0 +1 @@
+uid://dy10r7pfqy63v
diff --git a/game/scripts/input_setup.gd b/game/scripts/input_setup.gd
new file mode 100644
index 0000000..5c57097
--- /dev/null
+++ b/game/scripts/input_setup.gd
@@ -0,0 +1,35 @@
+class_name InputSetup
+extends RefCounted
+## Registers the game's input actions in code, so that project.godot holds no
+## serialized input events. Keys are physical positions, so WASD stays in
+## place on German keyboards too.
+
+
+static func install() -> void:
+	_add_keys("move_up", [KEY_W, KEY_UP])
+	_add_keys("move_down", [KEY_S, KEY_DOWN])
+	_add_keys("move_left", [KEY_A, KEY_LEFT])
+	_add_keys("move_right", [KEY_D, KEY_RIGHT])
+	_add_keys("save_game", [KEY_F5])
+	_add_keys("load_game", [KEY_F9])
+	_add_keys("toggle_pause", [KEY_ESCAPE])
+	_add_mouse_button("dig", MOUSE_BUTTON_LEFT)
+
+
+static func _add_keys(action: StringName, keys: Array[Key]) -> void:
+	if InputMap.has_action(action):
+		return
+	InputMap.add_action(action)
+	for key in keys:
+		var event := InputEventKey.new()
+		event.physical_keycode = key
+		InputMap.action_add_event(action, event)
+
+
+static func _add_mouse_button(action: StringName, button: MouseButton) -> void:
+	if InputMap.has_action(action):
+		return
+	InputMap.add_action(action)
+	var event := InputEventMouseButton.new()
+	event.button_index = button
+	InputMap.action_add_event(action, event)
diff --git a/game/scripts/input_setup.gd.uid b/game/scripts/input_setup.gd.uid
new file mode 100644
index 0000000..ffc4f91
--- /dev/null
+++ b/game/scripts/input_setup.gd.uid
@@ -0,0 +1 @@
+uid://dvckt6ss6k4xi
diff --git a/game/scripts/save_store.gd b/game/scripts/save_store.gd
new file mode 100644
index 0000000..a789d99
--- /dev/null
+++ b/game/scripts/save_store.gd
@@ -0,0 +1,93 @@
+class_name SaveStore
+extends RefCounted
+## The game's files on the player's machine: the player key, the save and
+## the session recordings for bug reports.
+
+const KEY_FILE := "player.key"
+const SAVE_FILE := "world.grw"
+const RECORDINGS_DIR := "recordings"
+## Recordings beyond this number are deleted, oldest first.
+const KEEP_RECORDINGS := 10
+const KEY_BYTES := 16
+
+var base_dir: String
+
+
+func _init(directory: String = "user://") -> void:
+	base_dir = directory
+	DirAccess.make_dir_recursive_absolute(base_dir)
+
+
+## The key that identifies this installation in every world. It is created
+## on first use and kept from then on.
+func player_key() -> PackedByteArray:
+	var path := base_dir.path_join(KEY_FILE)
+	var key := FileAccess.get_file_as_bytes(path)
+	if key.size() != KEY_BYTES:
+		key = Crypto.new().generate_random_bytes(KEY_BYTES)
+		_write(path, key)
+	return key
+
+
+func has_save() -> bool:
+	return FileAccess.file_exists(base_dir.path_join(SAVE_FILE))
+
+
+func read_save() -> PackedByteArray:
+	return FileAccess.get_file_as_bytes(base_dir.path_join(SAVE_FILE))
+
+
+## Writes the save through a temporary file, so that a crash while writing
+## never destroys the previous save. Returns false if nothing was written.
+func write_save(bytes: PackedByteArray) -> bool:
+	if bytes.is_empty():
+		return false
+	var path := base_dir.path_join(SAVE_FILE)
+	var temporary := path + ".tmp"
+	if not _write(temporary, bytes):
+		return false
+	return DirAccess.rename_absolute(temporary, path) == OK
+
+
+## Moves an unusable save out of the way, so that the next save does not
+## overwrite it. An older set-aside save is replaced. Returns the new path.
+func set_aside_save() -> String:
+	var path := base_dir.path_join(SAVE_FILE)
+	var aside := path + ".broken"
+	DirAccess.rename_absolute(path, aside)
+	return aside
+
+
+## Stores a session recording and deletes the oldest ones beyond
+## KEEP_RECORDINGS. Returns the path, or an empty text if nothing was written.
+func write_recording(bytes: PackedByteArray) -> String:
+	if bytes.is_empty():
+		return ""
+	var directory := base_dir.path_join(RECORDINGS_DIR)
+	DirAccess.make_dir_recursive_absolute(directory)
+	# Microseconds since 1970, padded so that names sort by age.
+	var stamp := int(Time.get_unix_time_from_system() * 1_000_000.0)
+	var path := directory.path_join("session-%016d.grwr" % stamp)
+	if not _write(path, bytes):
+		return ""
+	var names := recordings()
+	while names.size() > KEEP_RECORDINGS:
+		DirAccess.remove_absolute(directory.path_join(names[0]))
+		names.remove_at(0)
+	return path
+
+
+## File names of the stored recordings, oldest first.
+func recordings() -> PackedStringArray:
+	var names := DirAccess.get_files_at(base_dir.path_join(RECORDINGS_DIR))
+	names.sort()
+	return names
+
+
+func _write(path: String, bytes: PackedByteArray) -> bool:
+	var file := FileAccess.open(path, FileAccess.WRITE)
+	if file == null:
+		return false
+	file.store_buffer(bytes)
+	file.close()
+	return true
diff --git a/game/scripts/save_store.gd.uid b/game/scripts/save_store.gd.uid
new file mode 100644
index 0000000..cf4a620
--- /dev/null
+++ b/game/scripts/save_store.gd.uid
@@ -0,0 +1 @@
+uid://cbp4jkbdfyawm
diff --git a/game/tests/support/test_files.gd b/game/tests/support/test_files.gd
new file mode 100644
index 0000000..09d77d3
--- /dev/null
+++ b/game/tests/support/test_files.gd
@@ -0,0 +1,18 @@
+class_name TestFiles
+extends RefCounted
+## Temporary folders below user://tests for tests that write files, so that
+## tests never touch the player's real key, save or recordings.
+
+
+static func temporary_dir(label: String) -> String:
+	var path := "user://tests".path_join("%s-%d" % [label, Time.get_ticks_usec()])
+	DirAccess.make_dir_recursive_absolute(path)
+	return path
+
+
+static func remove_dir(path: String) -> void:
+	for file in DirAccess.get_files_at(path):
+		DirAccess.remove_absolute(path.path_join(file))
+	for directory in DirAccess.get_directories_at(path):
+		remove_dir(path.path_join(directory))
+	DirAccess.remove_absolute(path)
diff --git a/game/tests/support/test_files.gd.uid b/game/tests/support/test_files.gd.uid
new file mode 100644
index 0000000..c85ba14
--- /dev/null
+++ b/game/tests/support/test_files.gd.uid
@@ -0,0 +1 @@
+uid://cjpx0i0uknopn
diff --git a/game/tests/test_i18n.gd b/game/tests/test_i18n.gd
new file mode 100644
index 0000000..3fbbd78
--- /dev/null
+++ b/game/tests/test_i18n.gd
@@ -0,0 +1,35 @@
+extends TestCase
+
+
+func _by_locale() -> Dictionary:
+	var result := {}
+	for translation in I18n.load_translations(I18n.TEXTS_FILE):
+		result[translation.locale] = translation
+	return result
+
+
+func test_german_and_english_exist() -> void:
+	var translations := _by_locale()
+	check(translations.has("de"), "German")
+	check(translations.has("en"), "English")
+
+
+func test_every_text_exists_in_every_language() -> void:
+	var translations := _by_locale()
+	var german: Translation = translations["de"]
+	var english: Translation = translations["en"]
+	var keys := german.get_message_list()
+	keys.sort()
+	var english_keys := english.get_message_list()
+	english_keys.sort()
+	check_eq(english_keys, keys, "the same keys")
+	for key in keys:
+		check(not String(german.get_message(key)).is_empty(), "German text for %s" % key)
+		check(not String(english.get_message(key)).is_empty(), "English text for %s" % key)
+
+
+func test_the_stone_count_has_a_slot_for_the_number() -> void:
+	var translations := _by_locale()
+	for locale: String in translations:
+		var text := String(translations[locale].get_message("STONE_COUNT"))
+		check(text.contains("%d"), "%s: %s" % [locale, text])
diff --git a/game/tests/test_i18n.gd.uid b/game/tests/test_i18n.gd.uid
new file mode 100644
index 0000000..db8795b
--- /dev/null
+++ b/game/tests/test_i18n.gd.uid
@@ -0,0 +1 @@
+uid://qmoy6gvht6ba
diff --git a/game/tests/test_input_setup.gd b/game/tests/test_input_setup.gd
new file mode 100644
index 0000000..e6f5aae
--- /dev/null
+++ b/game/tests/test_input_setup.gd
@@ -0,0 +1,15 @@
+extends TestCase
+
+
+func test_every_action_of_the_game_exists() -> void:
+	InputSetup.install()
+	for action in ["move_up", "move_down", "move_left", "move_right", "dig", "save_game", "load_game", "toggle_pause"]:
+		check(InputMap.has_action(action), "action %s" % action)
+
+
+func test_installing_twice_adds_no_second_set_of_keys() -> void:
+	InputSetup.install()
+	var events := InputMap.action_get_events("move_up").size()
+	InputSetup.install()
+	check_eq(InputMap.action_get_events("move_up").size(), events, "same number of keys")
+	check_eq(events, 2, "W and the arrow key")
diff --git a/game/tests/test_input_setup.gd.uid b/game/tests/test_input_setup.gd.uid
new file mode 100644
index 0000000..6ac9610
--- /dev/null
+++ b/game/tests/test_input_setup.gd.uid
@@ -0,0 +1 @@
+uid://dxk7wymwduoy2
diff --git a/game/tests/test_save_store.gd b/game/tests/test_save_store.gd
new file mode 100644
index 0000000..7eb655a
--- /dev/null
+++ b/game/tests/test_save_store.gd
@@ -0,0 +1,56 @@
+extends TestCase
+
+
+func test_the_player_key_is_created_once_and_kept() -> void:
+	var directory := TestFiles.temporary_dir("key")
+	var first := SaveStore.new(directory).player_key()
+	var second := SaveStore.new(directory).player_key()
+	check_eq(first.size(), SaveStore.KEY_BYTES, "sixteen bytes")
+	check_eq(second, first, "the same key on the next start")
+	TestFiles.remove_dir(directory)
+
+
+func test_a_save_is_written_and_read_back() -> void:
+	var directory := TestFiles.temporary_dir("save")
+	var store := SaveStore.new(directory)
+	check(not store.has_save(), "no save at first")
+	check(store.write_save(PackedByteArray([1, 2, 3])), "written")
+	check(store.write_save(PackedByteArray([4, 5])), "overwritten")
+	check(store.has_save(), "a save exists")
+	check_eq(store.read_save(), PackedByteArray([4, 5]), "the newest save is read")
+	check(not FileAccess.file_exists(directory.path_join(SaveStore.SAVE_FILE + ".tmp")), "no temporary file is left")
+	TestFiles.remove_dir(directory)
+
+
+func test_an_empty_save_is_not_written() -> void:
+	var directory := TestFiles.temporary_dir("empty")
+	var store := SaveStore.new(directory)
+	check(not store.write_save(PackedByteArray()), "refused")
+	check(not store.has_save(), "no file")
+	TestFiles.remove_dir(directory)
+
+
+func test_an_unusable_save_can_be_set_aside() -> void:
+	var directory := TestFiles.temporary_dir("aside")
+	var store := SaveStore.new(directory)
+	store.write_save(PackedByteArray([9, 9]))
+	var aside := store.set_aside_save()
+	check(not store.has_save(), "the save is out of the way")
+	check_eq(FileAccess.get_file_as_bytes(aside), PackedByteArray([9, 9]), "its content is kept")
+	TestFiles.remove_dir(directory)
+
+
+func test_only_the_newest_recordings_are_kept() -> void:
+	var directory := TestFiles.temporary_dir("recordings")
+	var store := SaveStore.new(directory)
+	var paths: PackedStringArray = []
+	for number in SaveStore.KEEP_RECORDINGS + 2:
+		paths.append(store.write_recording(PackedByteArray([number])))
+		OS.delay_usec(10)
+	var names := store.recordings()
+	check_eq(names.size(), SaveStore.KEEP_RECORDINGS, "only the newest are kept")
+	check(not FileAccess.file_exists(paths[0]), "the oldest is gone")
+	check(not FileAccess.file_exists(paths[1]), "the second oldest is gone")
+	check(FileAccess.file_exists(paths[paths.size() - 1]), "the newest is there")
+	check_eq(store.write_recording(PackedByteArray()), "", "an empty recording is not written")
+	TestFiles.remove_dir(directory)
diff --git a/game/tests/test_save_store.gd.uid b/game/tests/test_save_store.gd.uid
new file mode 100644
index 0000000..0a1d0d2
--- /dev/null
+++ b/game/tests/test_save_store.gd.uid
@@ -0,0 +1 @@
+uid://cd4grmj44ifao