WPML allows you to hide languages on your site while preparing translations, ensuring incomplete content stays hidden.
To hide a language on the front-end, go to WPML → Settings → Languages. In the Manage and Hide Site Languages section, tick Hide on the row of every language you want to hide, then click Save.

Hiding language on front-end
Sending Content to Translation and Reviewing Translations for Languages That Are Hidden
To send content to translation for hidden languages, you have to change adjust one user profile setting for your translators first. This also applies if you need to allow translators to review and approve pending translations for these languages.
- Go to Users → All Users and click Edit next to a user that you want to see hidden languages.
- Find the WPML language settings section and tick the Display hidden languages checkbox.
- Click the Update Profile button to save.

Editing user profile settings
Now, you can assign translation jobs to this specific user and allow them to review translations for hidden languages.