diff --git a/Scripts/unused_strings.py b/Scripts/unused_strings.py
index eaf9771761..0e64c0b405 100755
--- a/Scripts/unused_strings.py
+++ b/Scripts/unused_strings.py
@@ -1,45 +1,100 @@
 #!/usr/bin/env python3
 """
-This script can be used to grep the source to tree to see which localized strings are in use. 
-
-author: corbett
-usage: ./unused_strings.py Localizable.strings source_dir
-eg:    ./unused_strings.py ../Signal/translations/en.lproj/Localizable.strings ../Signal/src
+Find unused localization strings.
 """
+
+import argparse
 import sys
 import os
 import re
+import pathlib
+from typing import Iterable
 
 
-def file_match(fname, pat):
-	try:
-		f = open(fname, "rt")
-	except IOError:
-		return
-
-	for i, line in enumerate(f):
-		if pat.search(line):
-			return True
-	f.close()
-	return False
+project_root = pathlib.Path(__file__).parent.parent.resolve()
+key_re = re.compile('^"([^"]+)" =')
 
 
-def rgrep_match(dir_name, s_pat):
-	pat = re.compile(s_pat)
-	for dirpath, dirnames, filenames in os.walk(dir_name):
-		for fname in filenames:
-			fullname = os.path.join(dirpath, fname)
-			match=file_match(fullname, pat)
-			if match:
-				return match
-	return False
+def project_path(from_root: str) -> pathlib.Path:
+    return project_root / from_root
 
-if __name__ == '__main__':
-	strings_file = sys.argv[1]
-	src_dir_name = sys.argv[2]
 
-	for item in open(strings_file).readlines():
-		grep_for = item.strip().split(' = ')[0].replace('"','')
-		if rgrep_match(src_dir_name, grep_for):
-			print(item.strip())
+def parse_args():
+    parser = argparse.ArgumentParser(description="Find unused localization strings.")
+    parser.add_argument(
+        "--strings",
+        type=pathlib.Path,
+        default=project_path("Signal/translations/en.lproj/Localizable.strings"),
+        help="A Localizable.strings file",
+    )
+    parser.add_argument(
+        "--src_dirs",
+        default=map(
+            project_path,
+            [
+                "Signal/src",
+                "SignalMessaging",
+                "SignalNSE",
+                "SignalServiceKit",
+                "SignalShareExtension",
+                "SignalUI",
+            ],
+        ),
+        nargs="+",
+        type=pathlib.Path,
+        help="One or more source directories",
+    )
+    return parser.parse_args()
 
+
+def get_all_keys(strings_file: pathlib.Path) -> Iterable[str]:
+    with open(strings_file, "r") as file:
+        for line in file:
+            match = key_re.match(line)
+            if match:
+                yield match.group(1)
+
+
+def get_all_file_paths(src_dir: os.PathLike) -> Iterable[str]:
+    for root, _, files in os.walk(src_dir):
+        for name in files:
+            yield os.path.join(root, name)
+
+
+def matching_substrings(file_path: str, substrings: Iterable[bytes]) -> Iterable[bytes]:
+    with open(file_path, "rb") as file:
+        contents = file.read()
+    return filter(lambda s: s in contents, substrings)
+
+
+def get_unused_keys(
+    strings_file: pathlib.Path, src_dirs: Iterable[pathlib.Path]
+) -> Iterable[str]:
+    all_keys = get_all_keys(strings_file)
+    all_keys_as_bytes = [key.encode() for key in all_keys]
+
+    keys_not_seen = set(all_keys_as_bytes)
+
+    for src_dir in src_dirs:
+        for file_path in get_all_file_paths(src_dir):
+            keys_seen = matching_substrings(file_path, keys_not_seen)
+            keys_not_seen -= set(keys_seen)
+
+    return map(lambda k: k.decode(), keys_not_seen)
+
+
+def main() -> None:
+    args = parse_args()
+
+    unused_keys = get_unused_keys(args.strings, args.src_dirs)
+    sorted_unused_keys = sorted(unused_keys)
+
+    for key in sorted_unused_keys:
+        print(key)
+
+    if len(sorted_unused_keys) != 0:
+        sys.exit(1)
+
+
+if __name__ == "__main__":
+    main()