diff --git a/src/web/file_cmds.py b/src/web/file_cmds.py
index 0605b30a..be6094ca 100644
--- a/src/web/file_cmds.py
+++ b/src/web/file_cmds.py
@@ -66,7 +66,7 @@ def list_images():
     command = proto.PbCommand()
     command.operation = proto.PbOperation.DEFAULT_IMAGE_FILES_INFO
     command.params["token"] = current_app.config["TOKEN"]
-    command.params["locale"] = session["language"]
+    command.params["locale"] = session["language"] or "en"
 
     data = send_pb_command(command.SerializeToString())
     result = proto.PbResult()
@@ -123,7 +123,7 @@ def create_new_image(file_name, file_type, size):
     command = proto.PbCommand()
     command.operation = proto.PbOperation.CREATE_IMAGE
     command.params["token"] = current_app.config["TOKEN"]
-    command.params["locale"] = session["language"]
+    command.params["locale"] = session["language"] or "en"
 
     command.params["file"] = file_name + "." + file_type
     command.params["size"] = str(size)
@@ -144,7 +144,7 @@ def delete_image(file_name):
     command = proto.PbCommand()
     command.operation = proto.PbOperation.DELETE_IMAGE
     command.params["token"] = current_app.config["TOKEN"]
-    command.params["locale"] = session["language"]
+    command.params["locale"] = session["language"] or "en"
 
     command.params["file"] = file_name
 
@@ -163,7 +163,7 @@ def rename_image(file_name, new_file_name):
     command = proto.PbCommand()
     command.operation = proto.PbOperation.RENAME_IMAGE
     command.params["token"] = current_app.config["TOKEN"]
-    command.params["locale"] = session["language"]
+    command.params["locale"] = session["language"] or "en"
 
     command.params["from"] = file_name
     command.params["to"] = new_file_name
diff --git a/src/web/ractl_cmds.py b/src/web/ractl_cmds.py
index 84371ac4..5373cd73 100644
--- a/src/web/ractl_cmds.py
+++ b/src/web/ractl_cmds.py
@@ -25,7 +25,7 @@ def get_server_info():
     command = proto.PbCommand()
     command.operation = proto.PbOperation.SERVER_INFO
     command.params["token"] = current_app.config["TOKEN"]
-    command.params["locale"] = session["language"]
+    command.params["locale"] = session["language"] or "en"
 
     data = send_pb_command(command.SerializeToString())
     result = proto.PbResult()
@@ -84,7 +84,7 @@ def get_reserved_ids():
     command = proto.PbCommand()
     command.operation = proto.PbOperation.RESERVED_IDS_INFO
     command.params["token"] = current_app.config["TOKEN"]
-    command.params["locale"] = session["language"]
+    command.params["locale"] = session["language"] or "en"
 
     data = send_pb_command(command.SerializeToString())
     result = proto.PbResult()
@@ -106,7 +106,7 @@ def get_network_info():
     command = proto.PbCommand()
     command.operation = proto.PbOperation.NETWORK_INTERFACES_INFO
     command.params["token"] = current_app.config["TOKEN"]
-    command.params["locale"] = session["language"]
+    command.params["locale"] = session["language"] or "en"
 
     data = send_pb_command(command.SerializeToString())
     result = proto.PbResult()
@@ -125,7 +125,7 @@ def get_device_types():
     command = proto.PbCommand()
     command.operation = proto.PbOperation.DEVICE_TYPES_INFO
     command.params["token"] = current_app.config["TOKEN"]
-    command.params["locale"] = session["language"]
+    command.params["locale"] = session["language"] or "en"
 
     data = send_pb_command(command.SerializeToString())
     result = proto.PbResult()
@@ -148,7 +148,7 @@ def get_image_files_info():
     command = proto.PbCommand()
     command.operation = proto.PbOperation.DEFAULT_IMAGE_FILES_INFO
     command.params["token"] = current_app.config["TOKEN"]
-    command.params["locale"] = session["language"]
+    command.params["locale"] = session["language"] or "en"
 
     data = send_pb_command(command.SerializeToString())
     result = proto.PbResult()
@@ -177,7 +177,7 @@ def attach_image(scsi_id, **kwargs):
     """
     command = proto.PbCommand()
     command.params["token"] = current_app.config["TOKEN"]
-    command.params["locale"] = session["language"]
+    command.params["locale"] = session["language"] or "en"
     devices = proto.PbDeviceDefinition()
     devices.id = int(scsi_id)
 
@@ -253,7 +253,7 @@ def detach_by_id(scsi_id, unit=None):
     command.operation = proto.PbOperation.DETACH
     command.devices.append(devices)
     command.params["token"] = current_app.config["TOKEN"]
-    command.params["locale"] = session["language"]
+    command.params["locale"] = session["language"] or "en"
 
     data = send_pb_command(command.SerializeToString())
     result = proto.PbResult()
@@ -269,7 +269,7 @@ def detach_all():
     command = proto.PbCommand()
     command.operation = proto.PbOperation.DETACH_ALL
     command.params["token"] = current_app.config["TOKEN"]
-    command.params["locale"] = session["language"]
+    command.params["locale"] = session["language"] or "en"
 
     data = send_pb_command(command.SerializeToString())
     result = proto.PbResult()
@@ -292,7 +292,7 @@ def eject_by_id(scsi_id, unit=None):
     command.operation = proto.PbOperation.EJECT
     command.devices.append(devices)
     command.params["token"] = current_app.config["TOKEN"]
-    command.params["locale"] = session["language"]
+    command.params["locale"] = session["language"] or "en"
 
     data = send_pb_command(command.SerializeToString())
     result = proto.PbResult()
@@ -312,7 +312,7 @@ def list_devices(scsi_id=None, unit=None):
     command = proto.PbCommand()
     command.operation = proto.PbOperation.DEVICES_INFO
     command.params["token"] = current_app.config["TOKEN"]
-    command.params["locale"] = session["language"]
+    command.params["locale"] = session["language"] or "en"
 
     # If method is called with scsi_id parameter, return the info on those devices
     # Otherwise, return the info on all attached devices
@@ -390,7 +390,7 @@ def reserve_scsi_ids(reserved_scsi_ids):
     command.operation = proto.PbOperation.RESERVE_IDS
     command.params["ids"] = ",".join(reserved_scsi_ids)
     command.params["token"] = current_app.config["TOKEN"]
-    command.params["locale"] = session["language"]
+    command.params["locale"] = session["language"] or "en"
 
     data = send_pb_command(command.SerializeToString())
     result = proto.PbResult()
@@ -408,7 +408,7 @@ def set_log_level(log_level):
     command.operation = proto.PbOperation.LOG_LEVEL
     command.params["level"] = str(log_level)
     command.params["token"] = current_app.config["TOKEN"]
-    command.params["locale"] = session["language"]
+    command.params["locale"] = session["language"] or "en"
 
     data = send_pb_command(command.SerializeToString())
     result = proto.PbResult()
@@ -426,7 +426,7 @@ def shutdown_pi(mode):
     command.operation = proto.PbOperation.SHUT_DOWN
     command.params["mode"] = str(mode)
     command.params["token"] = current_app.config["TOKEN"]
-    command.params["locale"] = session["language"]
+    command.params["locale"] = session["language"] or "en"
 
     data = send_pb_command(command.SerializeToString())
     result = proto.PbResult()
@@ -443,7 +443,7 @@ def is_token_auth():
     command = proto.PbCommand()
     command.operation = proto.PbOperation.CHECK_AUTHENTICATION
     command.params["token"] = current_app.config["TOKEN"]
-    command.params["locale"] = session["language"]
+    command.params["locale"] = session["language"] or "en"
 
     data = send_pb_command(command.SerializeToString())
     result = proto.PbResult()
diff --git a/src/web/web.py b/src/web/web.py
index 33a1c5d4..26fa58d8 100644
--- a/src/web/web.py
+++ b/src/web/web.py
@@ -92,10 +92,13 @@ def get_locale():
     try:
         language = session["language"]
     except KeyError:
-        language = None
-    if language is not None:
+        language = ""
+        logging.warning("The default locale could not be detected. Falling back to English.")
+    if language:
         return language
-    return request.accept_languages.best_match(LANGUAGES)
+    # Hardcoded fallback to "en" when the user agent does not send an accept-language header
+    language = request.accept_languages.best_match(LANGUAGES) or "en"
+    return language
 
 
 def get_supported_locales():