Hello Flexo,
For currently 1.2.0 They are located in https://github.com/hestiacp/hestiacp/blob/main/web/inc/i18n/ru.php
For 1.3.0 This will switched and they are located in https://github.com/hestiacp/hestiacp/tree/staging/features/web/locale
They can be changed via https://translate.hestiacp.com/projects/hestiacp/ru/default/
See also Official translations?