From MikroTik Wiki
< User Manager
New User Manager supports multiple languages.
- Download language file template, containing English translations
- Open it with poEdit. Language files are plain-text and can also be edited with any text editor if poEdit is not available.
- Translate the file
- Set the language:
- Save it as .lng file. File name is not important (.lng extension is required), but it is recommended to contain translation language information, for example de_DE.lng for German translation)
- Upload the file to router, using ftp
- If you are logged in to User Manager web, log out and log in again.
- There will be language select box on the menu. Select desired language.