diff --git a/libretranslate/app.py b/libretranslate/app.py
index b210a94..c1fd4ac 100644
--- a/libretranslate/app.py
+++ b/libretranslate/app.py
@@ -830,7 +830,7 @@ def create_app(args):
 
         src_lang = next(iter([l for l in languages if l.code == source_lang]), None)
 
-        if src_lang is None:
+        if src_lang is None and source_lang != "auto":
             abort(400, description=_("%(lang)s is not supported", lang=source_lang))
 
         tgt_lang = next(iter([l for l in languages if l.code == target_lang]), None)
@@ -852,6 +852,14 @@ def create_app(args):
             if char_limit > 0:
                 request.req_cost = max(1, int(os.path.getsize(filepath) / char_limit))
 
+            if source_lang == "auto":
+                src_texts = argostranslatefiles.get_texts(filepath)
+                candidate_langs = detect_languages(src_texts)
+                detected_src_lang = candidate_langs[0]
+                src_lang = next(iter([l for l in languages if l.code == detected_src_lang["language"]]), None)
+                if src_lang is None:
+                    abort(400, description=_("%(lang)s is not supported", lang=detected_src_lang["language"]))
+
             translated_file_path = argostranslatefiles.translate_file(src_lang.get_translation(tgt_lang), filepath)
             translated_filename = os.path.basename(translated_file_path)
 
diff --git a/pyproject.toml b/pyproject.toml
index 930e952..49709b5 100644
--- a/pyproject.toml
+++ b/pyproject.toml
@@ -48,7 +48,7 @@ dependencies = [
     "appdirs ==1.4.4",
     "APScheduler ==3.9.1",
     "translatehtml ==1.5.2",
-    "argos-translate-files ==1.1.4",
+    "argos-translate-files ==1.2.0",
     "itsdangerous ==2.1.2",
     "Werkzeug ==2.3.8",
     "requests ==2.31.0",