diff --git a/lua/cp/config.lua b/lua/cp/config.lua
index 1d7ec61..708969f 100644
--- a/lua/cp/config.lua
+++ b/lua/cp/config.lua
@@ -4,7 +4,7 @@
 ---@field debug? string[] Debug command template
 ---@field executable? string Executable name
 ---@field version? number Language version
----@field extension string File extension
+---@field extension? string File extension
 
 ---@class PartialLanguageConfig
 ---@field compile? string[] Compile command template
@@ -17,7 +17,7 @@
 ---@class ContestConfig
 ---@field cpp LanguageConfig
 ---@field python LanguageConfig
----@field default_language string
+---@field default_language? string
 
 ---@class PartialContestConfig
 ---@field cpp? PartialLanguageConfig
@@ -139,48 +139,7 @@ function M.setup(user_config)
                 return false
               end
 
-              for lang_name, lang_config in pairs(config) do
-                if type(lang_config) == 'table' then
-                  if
-                    lang_name ~= 'default_language'
-                    and not vim.tbl_contains(vim.tbl_keys(constants.canonical_filetypes), lang_name)
-                  then
-                    return false,
-                      ("Invalid language '%s'. Valid languages: %s"):format(
-                        lang_name,
-                        table.concat(vim.tbl_keys(constants.canonical_filetypes), ', ')
-                      )
-                  end
-
-                  if
-                    lang_config.extension
-                    and not vim.tbl_contains(
-                      vim.tbl_keys(constants.filetype_to_language),
-                      lang_config.extension
-                    )
-                  then
-                    return false,
-                      ("Invalid extension '%s'. Valid extensions: %s"):format(
-                        lang_config.extension,
-                        table.concat(vim.tbl_keys(constants.filetype_to_language), ', ')
-                      )
-                  end
-                end
-              end
-
-              if
-                config.default_language
-                and not vim.tbl_contains(
-                  vim.tbl_keys(constants.canonical_filetypes),
-                  config.default_language
-                )
-              then
-                return false,
-                  ("Invalid default_language '%s'. Valid languages: %s"):format(
-                    config.default_language,
-                    table.concat(vim.tbl_keys(constants.canonical_filetypes), ', ')
-                  )
-              end
+              -- Allow any language and extension configurations
 
               return true
             end,
diff --git a/spec/config_spec.lua b/spec/config_spec.lua
index e3011fc..b248fc5 100644
--- a/spec/config_spec.lua
+++ b/spec/config_spec.lua
@@ -157,7 +157,6 @@ describe('cp.config', function()
           contests = {
             test = {
               python = { test = { 'python3' } },
-              rust = { compile = { 'rustc' } },
             },
           },
         }
@@ -192,36 +191,27 @@ describe('cp.config', function()
 
         assert.has_error(function()
           config.setup(invalid_config)
-        end, 'No language configurations found for test')
+        end, 'No language configurations found')
       end)
 
-      it('validates language names against canonical_filetypes', function()
-        local invalid_config = {
-          contests = {
-            test = {
-              invalid_lang = { compile = { 'gcc' } },
-            },
-          },
-        }
-
-        assert.has_error(function()
-          config.setup(invalid_config)
-        end, "Invalid language 'invalid_lang'")
-      end)
-
-      it('validates default_language value', function()
-        local invalid_config = {
+      it('allows custom language names', function()
+        local user_config = {
           contests = {
             test = {
+              rust = {
+                compile = { 'rustc', '{source}', '-o', '{binary}' },
+                test = { '{binary}' },
+                extension = 'rs',
+              },
               cpp = { compile = { 'g++' } },
-              default_language = 'xd',
             },
           },
         }
 
-        assert.has_error(function()
-          config.setup(invalid_config)
-        end, "Invalid default_language 'xd'")
+        assert.has_no.errors(function()
+          local result = config.setup(user_config)
+          assert.equals('cpp', result.contests.test.default_language)
+        end)
       end)
     end)
   end)