diff --git a/.github/unused-strings.py b/.github/unused-strings.py
new file mode 100644
--- /dev/null
+++ b/.github/unused-strings.py
@@ -0,0 +1,221 @@
+"""
+Script to scan the OpenTTD source-tree for STR_ entries that are defined but
+no longer used.
+
+This is not completely trivial, as OpenTTD references a lot of strings in
+relation to another string. The most obvious example of this is a list. OpenTTD
+only references the first entry in the list, and does "+ <var>" to get to the
+correct string.
+
+There are other ways OpenTTD does use relative values. This script tries to
+account for all of them, to give the best approximation we have for "this
+string is unused".
+"""
+
+import glob
+import os
+import re
+import subprocess
+import sys
+
+from enum import Enum
+
+LENGTH_NAME_LOOKUP = {
+    "VEHICLE_TYPES": 4,
+}
+
+
+class SkipType(Enum):
+    NONE = 1
+    LENGTH = 2
+    EXTERNAL = 3
+    ZERO_IS_SPECIAL = 4
+    EXPECT_NEWLINE = 5
+
+
+def read_language_file(filename, strings_found, errors):
+    strings_defined = []
+
+    skip = SkipType.NONE
+    length = 0
+    common_prefix = ""
+    last_tiny_string = ""
+
+    with open(filename) as fp:
+        for line in fp.readlines():
+            if not line.strip():
+                if skip == SkipType.EXPECT_NEWLINE:
+                    skip = SkipType.NONE
+                continue
+
+            line = line.strip()
+
+            if skip == SkipType.EXPECT_NEWLINE:
+                # The only thing allowed after a list, is this next marker, or a newline.
+                if line == "###next-name-looks-similar":
+                    # "###next-name-looks-similar"
+                    # Indicates the common prefix of the last list has a very
+                    # similar name to the next entry, but isn't part of the
+                    # list. So do not emit a warning about them looking very
+                    # similar.
+
+                    if length != 0:
+                        errors.append(f"ERROR: list around {name} is shorted than indicated by ###length")
+
+                    common_prefix = ""
+                else:
+                    errors.append(f"ERROR: expected a newline after a list, but didn't find any around {name}. Did you add an entry to the list without increasing the length?")
+
+                skip = SkipType.NONE
+
+            if line[0] == "#":
+                if line.startswith("###length "):
+                    # "###length <count>"
+                    # Indicates the next few entries are part of a list. Only
+                    # the first entry is possibly referenced, and the rest are
+                    # indirectly.
+
+                    if length != 0:
+                        errors.append(f"ERROR: list around {name} is shorted than indicated by ###length")
+
+                    length = line.split(" ")[1].strip()
+
+                    if length.isnumeric():
+                        length = int(length)
+                    else:
+                        length = LENGTH_NAME_LOOKUP[length]
+
+                    skip = SkipType.LENGTH
+                elif line.startswith("###external "):
+                    # "###external <count>"
+                    # Indicates the next few entries are used outside the
+                    # source and will not be referenced.
+
+                    if length != 0:
+                        errors.append(f"ERROR: list around {name} is shorted than indicated by ###length")
+
+                    length = line.split(" ")[1].strip()
+                    length = int(length)
+
+                    skip = SkipType.EXTERNAL
+                elif line.startswith("###setting-zero-is-special"):
+                    # "###setting-zero-is-special"
+                    # Indicates the next entry is part of the "zero is special"
+                    # flag of settings. These entries are not referenced
+                    # directly in the code.
+
+                    if length != 0:
+                        errors.append(f"ERROR: list around {name} is shorted than indicated by ###length")
+
+                    skip = SkipType.ZERO_IS_SPECIAL
+
+                continue
+
+            name = line.split(":")[0].strip()
+            strings_defined.append(name)
+
+            # If a string ends on _TINY or _SMALL, it can be the {TINY} variant.
+            # Check for this by some fuzzy matching.
+            if name.endswith(("_SMALL", "_TINY")):
+                last_tiny_string = name
+            elif last_tiny_string:
+                matching_name = "_".join(last_tiny_string.split("_")[:-1])
+                if name == matching_name:
+                    strings_found.add(last_tiny_string)
+            else:
+                last_tiny_string = ""
+
+            if skip == SkipType.EXTERNAL:
+                strings_found.add(name)
+                skip = SkipType.LENGTH
+
+            if skip == SkipType.LENGTH:
+                skip = SkipType.NONE
+                length -= 1
+                common_prefix = name
+            elif skip == SkipType.ZERO_IS_SPECIAL:
+                strings_found.add(name)
+            elif length > 0:
+                strings_found.add(name)
+                length -= 1
+
+                # Find the common prefix of these strings
+                for i in range(len(common_prefix)):
+                    if common_prefix[0 : i + 1] != name[0 : i + 1]:
+                        common_prefix = common_prefix[0:i]
+                        break
+
+                if length == 0:
+                    skip = SkipType.EXPECT_NEWLINE
+
+                    if len(common_prefix) < 6:
+                        errors.append(f"ERROR: common prefix of block including {name} was reduced to {common_prefix}. This means the names in the list are not consistent.")
+            elif common_prefix:
+                if name.startswith(common_prefix):
+                    errors.append(f"ERROR: {name} looks a lot like block above with prefix {common_prefix}. This mostly means that the list length was too short. Use '###next-name-looks-similar' if it is not.")
+                common_prefix = ""
+
+    return strings_defined
+
+
+def scan_source_files(path, strings_found):
+    for new_path in glob.glob(f"{path}/*"):
+        if os.path.isdir(new_path):
+            scan_source_files(new_path, strings_found)
+            continue
+
+        if not new_path.endswith((".c", ".h", ".cpp", ".hpp", ".ini")):
+            continue
+
+        # Most files we can just open, but some use magic, that requires the
+        # G++ preprocessor before we can make sense out of it.
+        if new_path == "src/table/cargo_const.h":
+            p = subprocess.run(["g++", "-E", new_path], stdout=subprocess.PIPE)
+            output = p.stdout.decode()
+        else:
+            with open(new_path) as fp:
+                output = fp.read()
+
+        # Find all the string references.
+        matches = re.findall(r"[^A-Z_](STR_[A-Z0-9_]*)", output)
+        strings_found.update(matches)
+
+
+def main():
+    strings_found = set()
+    errors = []
+
+    scan_source_files("src", strings_found)
+    strings_defined = read_language_file("src/lang/english.txt", strings_found, errors)
+
+    # STR_LAST_STRINGID is special, and not really a string.
+    strings_found.remove("STR_LAST_STRINGID")
+    # These are mentioned in comments, not really a string.
+    strings_found.remove("STR_XXX")
+    strings_found.remove("STR_NEWS")
+    strings_found.remove("STR_CONTENT_TYPE_")
+
+    # This string is added for completion, but never used.
+    strings_defined.remove("STR_JUST_DATE_SHORT")
+
+    strings_defined = sorted(strings_defined)
+    strings_found = sorted(list(strings_found))
+
+    for string in strings_found:
+        if string not in strings_defined:
+            errors.append(f"ERROR: {string} found but never defined.")
+
+    for string in strings_defined:
+        if string not in strings_found:
+            errors.append(f"ERROR: {string} is (possibly) no longer needed.")
+
+    if errors:
+        for error in errors:
+            print(error)
+        sys.exit(1)
+    else:
+        print("OK")
+
+
+if __name__ == "__main__":
+    main()