diff --git a/Cargo.lock b/Cargo.lock
index 7098b88..dbc9592 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -166,7 +166,7 @@ dependencies = [
  "memchr",
  "serde",
  "serde_derive",
- "winnow 0.7.8",
+ "winnow 0.7.9",
 ]
 
 [[package]]
@@ -499,9 +499,9 @@ dependencies = [
 
 [[package]]
 name = "cc"
-version = "1.2.20"
+version = "1.2.21"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "04da6a0d40b948dfc4fa8f5bbf402b0fc1a64a28dbf7d12ffd683550f2c1b63a"
+checksum = "8691782945451c1c383942c4874dbe63814f61cb57ef773cda2972682b7bb3c0"
 dependencies = [
  "shlex",
 ]
@@ -592,13 +592,14 @@ dependencies = [
  "chrono",
  "ron",
  "serde",
+ "strum",
 ]
 
 [[package]]
 name = "comrak"
-version = "0.38.0"
+version = "0.39.0"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "f690706b5db081dccea6206d7f6d594bb9895599abea9d1a0539f13888781ae8"
+checksum = "d5c834ca54c5a20588b358f34d1533b4b498ddb5fd979cec6b22d0e8867a2449"
 dependencies = [
  "bon",
  "caseless",
@@ -1836,9 +1837,9 @@ checksum = "d750af042f7ef4f724306de029d18836c26c1765a54a6a3f094cbd23a7267ffa"
 
 [[package]]
 name = "libm"
-version = "0.2.13"
+version = "0.2.14"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "c9627da5196e5d8ed0b0495e61e518847578da83483c37288316d9b2e03a7f72"
+checksum = "a25169bd5913a4b437588a7e3d127cd6e90127b60e0ffbd834a38f1599e016b8"
 
 [[package]]
 name = "libsqlite3-sys"
@@ -2536,7 +2537,6 @@ dependencies = [
  "serde",
  "sqlx",
  "strum",
- "strum_macros",
  "thiserror 2.0.12",
  "tokio",
  "tower",
@@ -2548,9 +2548,9 @@ dependencies = [
 
 [[package]]
 name = "redox_syscall"
-version = "0.5.11"
+version = "0.5.12"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "d2f103c6d277498fbceb16e84d317e2a400f160f46904d5f5410848c829511a3"
+checksum = "928fca9cf2aa042393a8325b9ead81d2f0df4cb12e1e24cef072922ccd99c5af"
 dependencies = [
  "bitflags 2.9.0",
 ]
@@ -3268,6 +3268,9 @@ name = "strum"
 version = "0.27.1"
 source = "registry+https://github.com/rust-lang/crates.io-index"
 checksum = "f64def088c51c9510a8579e3c5d67c65349dcf755e5479ad3d010aa6454e2c32"
+dependencies = [
+ "strum_macros",
+]
 
 [[package]]
 name = "strum_macros"
@@ -4222,9 +4225,9 @@ dependencies = [
 
 [[package]]
 name = "winnow"
-version = "0.7.8"
+version = "0.7.9"
 source = "registry+https://github.com/rust-lang/crates.io-index"
-checksum = "9e27d6ad3dac991091e4d35de9ba2d2d00647c5d0fc26c5496dee55984ae111b"
+checksum = "d9fb597c990f03753e08d3c29efbfcf2019a003b4bf4ba19225c158e1549f0f3"
 dependencies = [
  "memchr",
 ]
diff --git a/backend/Cargo.toml b/backend/Cargo.toml
index 48f85b1..d627ad1 100644
--- a/backend/Cargo.toml
+++ b/backend/Cargo.toml
@@ -31,13 +31,12 @@ sqlx = { version = "0.8", features = ["sqlite", "runtime-tokio", "chrono"] }
 async-compression = { version = "0.4", features = ["tokio", "gzip"] }
 
 askama = "0.14"
-comrak = "0.38"
+comrak = "0.39"
 
 argon2 = { version = "0.5", features = ["default", "std"] }
 rand_core = { version = "0.9", features = ["std"] }
 rand = "0.9"
-strum = "0.27"
-strum_macros = "0.27"
+strum = { version = "0.27", features = ["derive"] }
 async-trait = "0.1"
 
 lettre = { version = "0.11", default-features = false, features = [
diff --git a/backend/src/app.rs b/backend/src/app.rs
index 4057bbb..bafaae5 100644
--- a/backend/src/app.rs
+++ b/backend/src/app.rs
@@ -233,6 +233,7 @@ pub fn make_service(
             "/shopping_list/checked",
             patch(services::ron::shopping_list::set_entry_checked),
         )
+        .route("/translation", get(services::ron::get_translation))
         .fallback(services::ron::not_found);
 
     let fragments_routes = Router::new().route(
diff --git a/backend/src/data/db/user.rs b/backend/src/data/db/user.rs
index 4ee1c59..10041ff 100644
--- a/backend/src/data/db/user.rs
+++ b/backend/src/data/db/user.rs
@@ -1,7 +1,7 @@
 use chrono::{Duration, prelude::*};
 use rand::distr::{Alphanumeric, SampleString};
 use sqlx::Sqlite;
-use strum_macros::Display;
+use strum::Display;
 
 use super::{Connection, DBError, Result};
 use crate::{
diff --git a/backend/src/services/ron/mod.rs b/backend/src/services/ron/mod.rs
index b971d8b..672464e 100644
--- a/backend/src/services/ron/mod.rs
+++ b/backend/src/services/ron/mod.rs
@@ -1,13 +1,18 @@
 use axum::{
     debug_handler,
-    extract::{Extension, State},
+    extract::{Extension, Query, State},
     http::{HeaderMap, StatusCode},
     response::{IntoResponse, Result},
 };
 use axum_extra::extract::cookie::{Cookie, CookieJar, SameSite};
+use common::ron_api;
 
 use crate::{
-    app::Context, consts, data::db, data::model, ron_extractor::ExtractRon, ron_utils::ron_error,
+    app::Context,
+    consts,
+    data::{db, model},
+    ron_extractor::ExtractRon,
+    ron_utils::{ron_error, ron_response_ok},
 };
 
 pub mod calendar;
@@ -36,6 +41,16 @@ pub async fn set_lang(
     Ok((jar, StatusCode::OK))
 }
 
+#[debug_handler]
+pub async fn get_translation(
+    Extension(context): Extension<Context>,
+    translation_id: Query<ron_api::Id>,
+) -> Result<impl IntoResponse> {
+    Ok(ron_response_ok(ron_api::Value {
+        value: context.tr.t_from_id(translation_id.id),
+    }))
+}
+
 /*** 404 ***/
 
 #[debug_handler]
diff --git a/backend/src/services/ron/shopping_list.rs b/backend/src/services/ron/shopping_list.rs
index 034ce8a..ca3b71a 100644
--- a/backend/src/services/ron/shopping_list.rs
+++ b/backend/src/services/ron/shopping_list.rs
@@ -58,7 +58,7 @@ pub async fn get(
 pub async fn set_entry_checked(
     State(connection): State<db::Connection>,
     Extension(context): Extension<Context>,
-    ExtractRon(ron): ExtractRon<ron_api::Value<bool>>,
+    ExtractRon(ron): ExtractRon<ron_api::KeyValue<bool>>,
 ) -> Result<impl IntoResponse> {
     check_user_rights_shopping_list_entry(&connection, &context.user, ron.id).await?;
     Ok(ron_response_ok(
diff --git a/backend/src/services/user.rs b/backend/src/services/user.rs
index 31c2630..25c9472 100644
--- a/backend/src/services/user.rs
+++ b/backend/src/services/user.rs
@@ -367,7 +367,15 @@ pub async fn sign_in_post(
                 .same_site(cookie::SameSite::Strict);
             Ok((
                 jar.add(cookie),
-                Redirect::to(&format!("/{}/", context.tr.current_lang_code())).into_response(),
+                Redirect::to(&format!(
+                    "/{}/?{}={}&{}={}",
+                    context.tr.current_lang_code(),
+                    common::consts::GET_PARAMETER_USER_MESSAGE,
+                    Sentence::SignInSuccess as i64,
+                    common::consts::GET_PARAMETER_USER_MESSAGE_LEVEL,
+                    common::toast::Level::Success as usize
+                ))
+                .into_response(),
             ))
         }
     }
diff --git a/backend/src/translation.rs b/backend/src/translation.rs
index a28f4e6..c9390ee 100644
--- a/backend/src/translation.rs
+++ b/backend/src/translation.rs
@@ -5,11 +5,11 @@ use common::utils;
 use ron::de::from_reader;
 use serde::Deserialize;
 use strum::EnumCount;
-use strum_macros::EnumCount;
 use tracing::warn;
 
 use crate::consts;
 
+#[repr(i64)]
 #[derive(Debug, Clone, EnumCount, Deserialize)]
 pub enum Sentence {
     MainTitle = 0,
@@ -34,6 +34,7 @@ pub enum Sentence {
     SignInMenu,
     SignInTitle,
     SignInButton,
+    SignInSuccess,
     WrongEmailOrPassword,
 
     // Sign up page.
@@ -188,6 +189,11 @@ impl Tr {
         self.lang.get(sentence)
     }
 
+    pub fn t_from_id(&self, sentence_id: i64) -> &'static str {
+        self.lang.get_from_id(sentence_id)
+    }
+
+    /// Translate a sentence with parameters.
     pub fn tp(&self, sentence: Sentence, params: &[Box<dyn ToString + Send>]) -> String {
         let text = self.lang.get(sentence);
         let params_as_string: Vec<String> = params.iter().map(|p| p.to_string()).collect();
@@ -246,6 +252,7 @@ impl Tr {
             | "VE" // Venezuela.
             | "ZW" // Zimbabwe.
             => Weekday::Sun,
+
             "AF" // Afghanistan.
             | "DZ" // Algeria.
             | "BH" // Bahrain.
@@ -262,6 +269,7 @@ impl Tr {
             | "AE" // United Arab Emirates.
             | "YE" // Yemen.
             => Weekday::Sat,
+
             _ => Weekday::Mon,
         }
     }
@@ -320,14 +328,17 @@ impl Language {
         T: Borrow<Sentence>,
     {
         let sentence_cloned: Sentence = sentence.borrow().clone();
+        self.get_from_id(sentence_cloned as i64)
+    }
 
-        let text: &str = match self.translation.get(sentence_cloned as usize) {
+    pub fn get_from_id(&'static self, sentence_id: i64) -> &'static str {
+        let text: &str = match self.translation.get(sentence_id as usize) {
             None => UNABLE_TO_FIND_TRANSLATION_MESSAGE,
             Some(text) => text,
         };
 
         if text.is_empty() && self.code != DEFAULT_LANGUAGE_CODE {
-            return get_language_translation(DEFAULT_LANGUAGE_CODE).get(sentence);
+            return get_language_translation(DEFAULT_LANGUAGE_CODE).get_from_id(sentence_id);
         }
         text
     }
diff --git a/backend/translation.ron b/backend/translation.ron
index e80e67e..993cc43 100644
--- a/backend/translation.ron
+++ b/backend/translation.ron
@@ -25,7 +25,9 @@
             (SignInMenu, "Sign in"),
             (SignInTitle, "Sign in"),
             (SignInButton, "Sign in"),
+            (SignInSuccess, "Sign in successful"),
             (WrongEmailOrPassword, "Wrong email or password"),
+
             (AccountMustBeValidatedFirst, "This account must be validated first"),
             (InvalidEmail, "Invalid email"),
             (PasswordDontMatch, "Passwords don't match"),
@@ -175,7 +177,9 @@
             (SignInMenu, "Se connecter"),
             (SignInTitle, "Se connecter"),
             (SignInButton, "Se connecter"),
+            (SignInSuccess, "Connexion réussie"),
             (WrongEmailOrPassword, "Mot de passe ou email invalide"),
+
             (AccountMustBeValidatedFirst, "Ce compte doit d'abord être validé"),
             (InvalidEmail, "Adresse email invalide"),
             (PasswordDontMatch, "Les mots de passe ne correspondent pas"),
diff --git a/common/Cargo.toml b/common/Cargo.toml
index 1fc4080..5299ea7 100644
--- a/common/Cargo.toml
+++ b/common/Cargo.toml
@@ -8,3 +8,4 @@ edition = "2024"
 ron = "0.10"
 serde = { version = "1.0", features = ["derive"] }
 chrono = { version = "0.4", features = ["serde"] }
+strum = { version = "0.27", features = ["derive"] }
diff --git a/common/src/consts.rs b/common/src/consts.rs
index f6d3af3..b8b09e7 100644
--- a/common/src/consts.rs
+++ b/common/src/consts.rs
@@ -1,2 +1,5 @@
 pub const MIN_PASSWORD_SIZE: usize = 8;
 pub const COOKIE_DARK_THEME: &str = "dark_theme";
+
+pub const GET_PARAMETER_USER_MESSAGE: &str = "user_message";
+pub const GET_PARAMETER_USER_MESSAGE_LEVEL: &str = "user_message_icon";
diff --git a/common/src/lib.rs b/common/src/lib.rs
index 63c9595..07b6d84 100644
--- a/common/src/lib.rs
+++ b/common/src/lib.rs
@@ -1,3 +1,4 @@
 pub mod consts;
 pub mod ron_api;
+pub mod toast;
 pub mod utils;
diff --git a/common/src/ron_api.rs b/common/src/ron_api.rs
index 87ca32c..596fbe3 100644
--- a/common/src/ron_api.rs
+++ b/common/src/ron_api.rs
@@ -19,9 +19,15 @@ pub struct Id {
     pub id: i64,
 }
 
-// A value associated with an id.
+// A simple value.
 #[derive(Serialize, Deserialize, Clone)]
 pub struct Value<T> {
+    pub value: T,
+}
+
+// A value associated with an id.
+#[derive(Serialize, Deserialize, Clone)]
+pub struct KeyValue<T> {
     pub id: i64,
     pub value: T,
 }
diff --git a/common/src/toast.rs b/common/src/toast.rs
new file mode 100644
index 0000000..4258a87
--- /dev/null
+++ b/common/src/toast.rs
@@ -0,0 +1,10 @@
+use strum::FromRepr;
+
+#[derive(FromRepr)]
+pub enum Level {
+    Success,
+    Error,
+    Info,
+    Warning,
+    Unknown,
+}
diff --git a/frontend/Cargo.toml b/frontend/Cargo.toml
index b00b241..7c39b7f 100644
--- a/frontend/Cargo.toml
+++ b/frontend/Cargo.toml
@@ -36,6 +36,7 @@ web-sys = { version = "0.3", features = [
     "DataTransfer",
     "DomRect",
     "KeyboardEvent",
+    "History",
     "Element",
     "DomStringMap",
     "HtmlDocument",
diff --git a/frontend/src/lib.rs b/frontend/src/lib.rs
index e085200..c0567c3 100644
--- a/frontend/src/lib.rs
+++ b/frontend/src/lib.rs
@@ -65,6 +65,44 @@ pub fn main() -> Result<(), JsValue> {
         _ => log!("Path unknown: ", location),
     }
 
+    // User message handling.
+    let user_message_params = utils::extract_get_parameters(&[
+        common::consts::GET_PARAMETER_USER_MESSAGE,
+        common::consts::GET_PARAMETER_USER_MESSAGE_LEVEL,
+    ]);
+    if let Some(mess_id) = user_message_params.iter().find_map(|(k, v)| {
+        if k == common::consts::GET_PARAMETER_USER_MESSAGE {
+            v.parse::<i64>().ok()
+        } else {
+            None
+        }
+    }) {
+        let level_id = user_message_params.iter().find_map(|(k, v)| {
+            if k == common::consts::GET_PARAMETER_USER_MESSAGE_LEVEL {
+                v.parse::<usize>().ok()
+            } else {
+                None
+            }
+        });
+
+        // Request the message to display.
+        spawn_local(async move {
+            let translation: ron_api::Value<String> =
+                request::get("translation", ron_api::Id { id: mess_id })
+                    .await
+                    .unwrap();
+            if let Some(level_id) = level_id {
+                toast::show_message_level(
+                    common::toast::Level::from_repr(level_id)
+                        .unwrap_or(common::toast::Level::Unknown),
+                    &translation.value,
+                );
+            } else {
+                toast::show_message(&translation.value);
+            }
+        });
+    }
+
     // Language handling.
     let select_language: HtmlSelectElement = by_id("select-website-language");
     EventListener::new(&select_language.clone(), "input", move |_event| {
diff --git a/frontend/src/shopping_list.rs b/frontend/src/shopping_list.rs
index 39f59c0..9674b1d 100644
--- a/frontend/src/shopping_list.rs
+++ b/frontend/src/shopping_list.rs
@@ -39,7 +39,7 @@ impl ShoppingList {
         } else {
             request::patch(
                 "shopping_list/checked",
-                ron_api::Value {
+                ron_api::KeyValue {
                     id: item_id,
                     value: is_checked,
                 },
diff --git a/frontend/src/toast.rs b/frontend/src/toast.rs
index faaff59..dd41a3d 100644
--- a/frontend/src/toast.rs
+++ b/frontend/src/toast.rs
@@ -1,16 +1,9 @@
+pub use common::toast::Level;
 use gloo::{events::EventListener, timers::callback::Timeout};
 use web_sys::{Element, HtmlElement, HtmlImageElement};
 
 use crate::utils::{SelectorExt, by_id, selector_and_clone};
 
-pub enum Level {
-    Success,
-    Error,
-    Info,
-    Warning,
-    Unknown,
-}
-
 const TIME_ANIMATION: u32 = 500; // [ms].
 const TIME_DISPLAYED: u32 = 5_000; // [ms].
 
diff --git a/frontend/src/utils.rs b/frontend/src/utils.rs
index 3fbb3bf..ea68d51 100644
--- a/frontend/src/utils.rs
+++ b/frontend/src/utils.rs
@@ -1,7 +1,7 @@
 use std::str::FromStr;
 
 use chrono::Locale;
-use gloo::utils::document;
+use gloo::utils::{document, window};
 use wasm_bindgen::prelude::*;
 use web_sys::Element;
 
@@ -133,3 +133,45 @@ pub fn get_locale() -> Locale {
         .replace("-", "_");
     Locale::from_str(&lang_and_territory).unwrap_or_default()
 }
+
+/// Extracts and remove some URL parameters from the current URL.
+pub fn extract_get_parameters(names: &[&str]) -> Vec<(String, String)> {
+    let mut param_values = vec![];
+    let location = window().location();
+
+    if let Ok(search) = location.search() {
+        if !search.is_empty() && search.starts_with('?') {
+            let mut search_chars = search.chars();
+            search_chars.next(); // To remove the first character which is '?'.
+            let mut new_search = String::with_capacity(search.len());
+            for kv in search_chars.as_str().split('&') {
+                match kv.split('=').collect::<Vec<&str>>()[..] {
+                    [key, value] if names.contains(&key) => {
+                        param_values.push((key.to_string(), value.to_string()));
+                    }
+                    _ => {
+                        if !new_search.is_empty() {
+                            new_search.push('&');
+                        }
+                        new_search.push_str(kv);
+                    }
+                }
+            }
+
+            if !param_values.is_empty() {
+                let mut new_url = location.pathname().unwrap();
+                if !new_search.is_empty() {
+                    new_url.push('?');
+                    new_url.push_str(&new_search);
+                }
+                window()
+                    .history()
+                    .unwrap()
+                    .push_state_with_url(&JsValue::null(), "", Some(&new_url))
+                    .unwrap();
+            }
+        }
+    }
+
+    param_values
+}