I know Greek (passport), English, and basic Russian
Greek and English have many common letters. (because many languages have the Latin alphabet, which is a copy of the Greek alphabet.
Latins (Roman) won Greeks but at the end learned Greek literature.
The Russian alphabet was created from Sent Methodios and Send Kyrillos. Both were monks and Professors to the first university of West in Konstantinoupolis.
The alphabet has changed 2–3 times but each initial version has Greek and Hebrew letters.
There are two groups of languages the Latin origin and the others. If you know a Latin origin language you can learn another sister language in 600 hours.
In the second group there are Russian, Chinese, Juponish and more, for this group there are different alphabets and you need more than 1200 hrs.
From Chinese to English is easy but from English to Chinese difficult.
