Is it permissible to correspond with foreign women via email or WhatsApp, without hearing their voice or seeing their picture, for the purpose of learning the English language?

If the conversation is general and involves a group of people, with no privacy between a man and a non-mahram woman, then there is no harm in it. However, if the conversation is only between the two of them, it could be a pretext for temptation (fitnah), because the Shari'ah came to block means to evil. Both men and women have an innate attraction to each other. The Prophet, peace and blessings be upon him, warned against the temptation of women, saying: "I have not left behind me any temptation more harmful to men than women," and "Beware of the world and beware of women, for the first temptation of the Children of Israel was with women." The objective of learning a language can be achieved through other means that are free from Shari'ah prohibitions, such as using recorded audio.