When comparing FSI Language Courses vs Readlang, the Slant community recommends Readlang for most people. In the question“What are the best sites for learning foreign languages?” Readlang is ranked 4th while FSI Language Courses is ranked 25th. The most important reason people chose Readlang is:
You can read any content in your target language using the browser extension, and translate any words/sentences you don't know quickly.
Specs
Ranked in these QuestionsQuestion Ranking
Pros
Pro Available for some less-common languages including Thai
Pro Free
Pro Good for learners at all levels
Pro High-quality content
Pro Fast-paced
Pro Translates native content quickly
You can read any content in your target language using the browser extension, and translate any words/sentences you don't know quickly.
Pro Creates flashcards from words you don't know
Readlang takes the words you translate most often and turns them into flashcards for you to practice.
Pro You can import long texts, including whole books
This is impossible or very annoying with other similar services.
Cons
Con Includes some outdated vocabulary
Con Created for American diplomats, so includes some specialized vocabulary that is less relevant to other learners
Con Some drills are too repetitive and boring
Con Not a good way to learn a language by itself
It's not your standard learning website with structured courses. Instead, it helps you get more familiar with your target language by translating content when needed.
This can be really beneficial for someone trying to improve their fluency, but isn't going to directly teach you grammar. Readlang is better used to supplement your learning while learning from structured courses.