diff --git a/src/language.rs b/src/language.rs
deleted file mode 100644
index 2d124a5..0000000
--- a/src/language.rs
+++ /dev/null
@@ -1,34 +0,0 @@
-use axum::async_trait;
-use axum::extract::FromRequestParts;
-use axum::http::{HeaderValue, StatusCode};
-use axum::http::header::ACCEPT_LANGUAGE;
-use axum::http::request::Parts;
-use serde::Deserialize;
-
-#[derive(Deserialize, Debug, Default)]
-pub enum Language {
-    #[default]
-    #[serde(rename = "en")]
-    En,
-    #[serde(rename = "nb")]
-    Nb,
-}
-
-#[derive(Debug)]
-pub(crate) struct AcceptLanguage(HeaderValue);
-
-#[async_trait]
-impl<S> FromRequestParts<S> for AcceptLanguage
-    where
-        S: Send + Sync,
-{
-    type Rejection = (StatusCode, &'static str);
-
-    async fn from_request_parts(parts: &mut Parts, _state: &S) -> Result<Self, Self::Rejection> {
-        if let Some(accept_language) = parts.headers.get(ACCEPT_LANGUAGE) {
-            Ok(AcceptLanguage(accept_language.clone()))
-        } else {
-            Err((StatusCode::BAD_REQUEST, "`Accept-language` header is missing"))
-        }
-    }
-}
diff --git a/src/main.rs b/src/main.rs
index 151d226..e7ce8df 100644
--- a/src/main.rs
+++ b/src/main.rs
@@ -11,7 +11,6 @@ use crate::routing::{index, simplify, table};
 mod expressions;
 mod parsing;
 mod routing;
-mod language;
 mod config;
 mod utils;
 
diff --git a/src/routing/error.rs b/src/routing/error.rs
index 7a2c94b..d15d2de 100644
--- a/src/routing/error.rs
+++ b/src/routing/error.rs
@@ -2,15 +2,31 @@ use axum::Json;
 use axum::response::{IntoResponse, Response};
 use serde::Serialize;
 
+#[derive(Serialize, Default)]
+#[serde(rename_all = "SCREAMING_SNAKE_CASE")]
+pub enum ErrorKind {
+    /// The syntax of the expression is invalid.
+    InvalidExpression,
+    /// The expression is too long.
+    LimitExceeded,
+    /// The expression is missing a character to be considered valid.
+    MissingCharacter,
+    /// Unexpected error.
+    #[default]
+    Unexpected,
+}
+
 #[derive(Serialize)]
 pub struct Error {
     pub message: String,
+    pub kind: ErrorKind,
 }
 
 impl Error {
-    pub fn new(message: impl Into<String>) -> Self {
+    pub fn new(message: impl Into<String>, kind: ErrorKind) -> Self {
         Self {
             message: message.into(),
+            kind,
         }
     }
 }
diff --git a/src/routing/response.rs b/src/routing/response.rs
index fc08402..1539a35 100644
--- a/src/routing/response.rs
+++ b/src/routing/response.rs
@@ -1,6 +1,7 @@
 use axum::Json;
 use axum::response::{IntoResponse, Response};
 use serde::Serialize;
+
 use crate::expressions::expression::Expression;
 use crate::expressions::truth_table::TruthTable;
 
diff --git a/src/routing/simplify.rs b/src/routing/simplify.rs
index 87f241c..42b5cf0 100644
--- a/src/routing/simplify.rs
+++ b/src/routing/simplify.rs
@@ -7,8 +7,7 @@ use serde::Deserialize;
 use crate::expressions::expression::Expression;
 use crate::expressions::simplify::Simplify;
 use crate::expressions::truth_table::{TruthTable, TruthTableOptions};
-use crate::language::{AcceptLanguage, Language};
-use crate::routing::error::Error;
+use crate::routing::error::{Error, ErrorKind};
 use crate::routing::response::SimplifyResponse;
 
 pub fn router() -> Router<()> {
@@ -26,8 +25,6 @@ const fn default_true() -> bool {
 
 #[derive(Deserialize)]
 struct QueryOptions {
-    #[serde(default)]
-    lang: Language,
     #[serde(default = "default_true")]
     simplify: bool,
     #[serde(default = "default_true")]
@@ -35,7 +32,7 @@ struct QueryOptions {
 }
 
 // TODO
-async fn simplify(Path(path): Path<String>, query: Query<QueryOptions>, accept_language: Option<AcceptLanguage>) -> Response {
+async fn simplify(Path(path): Path<String>, query: Query<QueryOptions>) -> Response {
     if let Ok(mut expression) = Expression::try_from(path.as_str()) {
         let before = expression.to_string();
         if query.simplify {
@@ -49,11 +46,11 @@ async fn simplify(Path(path): Path<String>, query: Query<QueryOptions>, accept_l
             truth_table: None,
         }.into_response()
     } else {
-        (StatusCode::BAD_REQUEST, Error::new("Invalid expression")).into_response()
+        (StatusCode::BAD_REQUEST, Error::new("Invalid expression", ErrorKind::InvalidExpression)).into_response()
     }
 }
 
-async fn simplify_and_table(Path(path): Path<String>, query: Query<QueryOptions>, accept_language: Option<AcceptLanguage>) -> Response {
+async fn simplify_and_table(Path(path): Path<String>, query: Query<QueryOptions>) -> Response {
     if let Ok(mut expression) = Expression::try_from(path.as_str()) {
         let before = expression.to_string();
         if query.simplify {
@@ -69,6 +66,6 @@ async fn simplify_and_table(Path(path): Path<String>, query: Query<QueryOptions>
             truth_table: Some(truth_table),
         }.into_response()
     } else {
-        (StatusCode::BAD_REQUEST, Error::new("Invalid expression")).into_response()
+        (StatusCode::BAD_REQUEST, Error::new("Invalid expression", ErrorKind::InvalidExpression)).into_response()
     }
 }