The appearance of the specified error is related to the lack of free space on the disk. The system requires space to create a web session. User files, backups from the control panel, site files, and log files take up space, so when logging into Vesta, the user may encounter the error NO LANGUAGE DEFINED. First of all, it is necessary to check the disk.
If the space is occupied by 98-100%, it should be cleaned of unnecessary files. For this purpose, FTP, SFTP, SSH, and other protocols are used.
Among the options is changing the tariff plan. This is relevant for VDS. As a result, the disk space on the server will increase.