I’ve used it for German and am now quite a bit into the Spanish lessons. It’s a very good site. It’s like “Rosetta Stone Lite.” I find that Rosetta Stone is better for conversation and Duolingo is good at getting my reading ability to increase faster. But everyone has different learning styles. The US foreign services language courses are also online and ree now. They’re somewhat outdated, but yet another good way to prepare for immersion.