For anyone interested in the Greek translation, these days we are organizing a group to help translate backtrop into the Greek language.
The team consists of members who had done a large part of the Greek translation for Drupal 7.
Those who are interested and can contribute to the translation project can register at https://localize.backdropcms.org/translate/languages/el/
We also have a discussion here #Greek - Backdrop CMS - Zulip (zulipchat.com)
Join with us !