Add the localize utility function.

utilities/localize.typ

@@ -0,0 +1,24 @@
+// Get the localized item of a given key inside a data dictionary, using the
+// provided language.
+#let localize(data, key, language) = {
+  // If the key is directly available in the data then it hasn't been localized.
+  if key in data {
+    return data.at(key)
+  }
+
+  // Then check for the key with the wanted language appended to it.
+  let key_with_language = key + "_" + language
+  if key_with_language in data {
+    return data.at(key_with_language)
+  }
+
+  // If a locale dictionary exists in the data, then run this function again
+  // using that dictionary for the same key and language.
+  if "locale" in data {
+    return localize(data.locale, key, language)
+  }
+
+  // And if the key nor locale exists in any way then panic, as we won't have
+  // any text to return.
+  panic("Data does not contain key in any localized way: " + key, data)
+}