Babbel is a platform, which combines self-paced tutorials and exercises with an online learning community. The tutorials are entertaining and include many different themes. There are several levels (although they don't appear to go beyond intermediate levels). You can study French, Spanish, Italian, English and German. Furthermore, you can interact with native people of the language you are studying--you can submit work and receive feedback from people who are native speakers of that language. The tandem component means you can be matched with a person who wants to learn the language you speak as a first language and he or she will be a native speaker of the language you wish to learn, which is a great way to learn a language and see language learning from a different perspective. Interaction can be synchronous (group and private chat) and delayed (discussion board and messages)--there is no need to provide your private email or telephone number. As membership is open to anyone who sets up an account, students would need to be advised to use caution when interacting within the site and also advised that all feedback given be double checked against other sources to verify the information is correct.
Of note: Idioms in several languages, including Russian. https://www.babbel.com/en/magazine/16-colorful-idioms-that-ll-sell-you-on-the-russian-language