In local installation by default use the EFI locale

When connecting remotely it still prefers the browser language

live/root/root/.icewm/startup

@@ -5,5 +5,21 @@ TOKEN_FILE=/run/agama/token
 TOKEN=$(cat $TOKEN_FILE)
 PREFS=$HOME/.mozilla/firefox/profile/user.js
 
-sed -e "s/__HOMEPAGE__/http:\/\/localhost\/login?token=$TOKEN/" $PREFS.template > $PREFS
+# read the system locale from EFI if present
+LANG_FILE=/sys/firmware/efi/efivars/PlatformLang-8be4df61-93ca-11d2-aa0d-00e098032b8c
+
+# file exists and is not empty
+if [ -s  "$LANG_FILE" ]; then
+  # skip the first 4 bytes (the EFI attributes), keep only the characters allowed in a language code,
+  # especially remove the trailing null byte
+  EFI_LANG=$(cat "$LANG_FILE" | tail -c +5 | tr -cd "[_a-zA-Z-]")
+
+  if [ -n "$EFI_LANG" ]; then
+    # escape & because it has a special meaning in sed replacement
+    LANG_QUERY="\\&lang=$EFI_LANG"
+  fi
+fi
+
+sed -e "s/__HOMEPAGE__/http:\/\/localhost\/login?token=$TOKEN$LANG_QUERY/" $PREFS.template > $PREFS
+
 firefox --kiosk --profile $HOME/.mozilla/firefox/profile

rust/agama-server/src/web/http.rs

@@ -100,10 +100,12 @@ pub async fn login(
 pub struct LoginFromQueryParams {
     /// Token to use for authentication.
     token: String,
+    /// Requested locale
+    lang: String,
 }
 
 #[utoipa::path(get, path = "/login", responses(
-    (status = 301, description = "Injects the authentication cookie if correct and redirects to the web UI")
+    (status = 307, description = "Injects the authentication cookie if correct and redirects to the web UI")
 ))]
 pub async fn login_from_query(
     State(state): State<ServiceState>,
@@ -120,7 +122,21 @@ pub async fn login_from_query(
         );
     }
 
-    headers.insert(header::LOCATION, HeaderValue::from_static("/"));
+    // the redirection path
+    let mut target = String::from("/");
+
+    // keep the "lang" URL query if it was present in the original request
+    if !&params.lang.is_empty() {
+        target.push_str(format!("?lang={}", params.lang).as_str());
+    }
+
+    let location = HeaderValue::from_str(target.as_str());
+
+    headers.insert(
+        header::LOCATION,
+        location.unwrap_or(HeaderValue::from_static("/")),
+    );
+
     (StatusCode::TEMPORARY_REDIRECT, headers)
 }