diff --git a/services/backend/src/routes/users.ts b/services/backend/src/routes/users.ts
index 836f77f5af..516b677c15 100644
--- a/services/backend/src/routes/users.ts
+++ b/services/backend/src/routes/users.ts
@@ -4,6 +4,8 @@ import { roles } from '../config/roles'
 import * as auth from '../middleware/auth'
 import { sendNotificationAboutAccessToUser, previewNotificationAboutAccessToUser } from '../services/mailService'
 import * as userService from '../services/userService'
+import { LANGUAGE_CODES } from '../shared/language'
+import { Language } from '../types'
 import logger from '../util/logger'
 
 const router = Router()
@@ -101,7 +103,7 @@ router.delete('/:uid/elements', auth.roles(['admin']), async (req: ElementsReque
 
 interface ChangeLanguageRequest extends Request {
   body: {
-    language: string
+    language: Language
   }
 }
 
@@ -109,7 +111,7 @@ router.post('/language', async (req: ChangeLanguageRequest, res: Response) => {
   const {
     body: { language },
   } = req
-  if (!['fi', 'sv', 'en'].includes(language)) {
+  if (!LANGUAGE_CODES.includes(language)) {
     return res.status(400).json('Invalid language')
   }
   try {
diff --git a/services/frontend/src/components/LanguagePicker/index.jsx b/services/frontend/src/components/LanguagePicker/index.jsx
index 9080aa4e90..7ab00d08bb 100644
--- a/services/frontend/src/components/LanguagePicker/index.jsx
+++ b/services/frontend/src/components/LanguagePicker/index.jsx
@@ -1,6 +1,6 @@
 import { Dropdown } from 'semantic-ui-react'
 
-import { LANGUAGE_CODES } from '@/constants'
+import { LANGUAGE_CODES } from '@/shared/language'
 import { useLanguage } from './useLanguage'
 
 export const LanguagePicker = () => {
diff --git a/services/frontend/src/components/LanguagePicker/useLanguage.jsx b/services/frontend/src/components/LanguagePicker/useLanguage.jsx
index 93d16b2d7c..02e66a19f4 100644
--- a/services/frontend/src/components/LanguagePicker/useLanguage.jsx
+++ b/services/frontend/src/components/LanguagePicker/useLanguage.jsx
@@ -1,8 +1,8 @@
 import { createContext, useState, useCallback, useContext, useEffect } from 'react'
 
-import { DEFAULT_LANG, LANGUAGE_CODES } from '@/constants'
 import { useGetAuthorizedUserQuery } from '@/redux/auth'
 import { useModifyLanguageMutation } from '@/redux/users'
+import { DEFAULT_LANG, LANGUAGE_CODES } from '@/shared/language'
 
 const LanguageContext = createContext([[], () => {}])
 LanguageContext.displayName = 'Language'
diff --git a/services/frontend/src/constants/index.js b/services/frontend/src/constants/index.js
index 7ae09560f7..d1dc63b621 100644
--- a/services/frontend/src/constants/index.js
+++ b/services/frontend/src/constants/index.js
@@ -1,5 +1,3 @@
-export const DEFAULT_LANG = 'fi'
-
 export const PRIORITYCODE_TEXTS = {
   1: 'Main',
   2: 'Secondary',
@@ -10,5 +8,3 @@ export const PRIORITYCODE_TEXTS = {
 // Increment this if search history code changes
 // so it will be reseted for all users.
 export const SEARCH_HISTORY_VERSION = '1.0'
-
-export const LANGUAGE_CODES = ['fi', 'en', 'sv']
diff --git a/services/frontend/src/redux/settings.js b/services/frontend/src/redux/settings.js
index af506a4539..1980fecefd 100644
--- a/services/frontend/src/redux/settings.js
+++ b/services/frontend/src/redux/settings.js
@@ -1,4 +1,4 @@
-import { DEFAULT_LANG } from '@/constants'
+import { DEFAULT_LANG } from '@/shared/language'
 
 const initialState = {
   language: DEFAULT_LANG,
diff --git a/services/shared/language.ts b/services/shared/language.ts
new file mode 100644
index 0000000000..8f61d41731
--- /dev/null
+++ b/services/shared/language.ts
@@ -0,0 +1,2 @@
+export const DEFAULT_LANG = 'fi'
+export const LANGUAGE_CODES = ['fi', 'en', 'sv'] as const
diff --git a/services/shared/tsconfig.json b/services/shared/tsconfig.json
index aa444cea28..1ba4d00eec 100644
--- a/services/shared/tsconfig.json
+++ b/services/shared/tsconfig.json
@@ -19,5 +19,5 @@
     "inlineSources": true,
     "resolveJsonModule": true
   },
-  "include": ["util/**/*", "index.ts"]
+  "include": ["**/*.ts"]
 }