There isn't really an "answer" to efficient learning other than consistent exposure, imo.
I was an Arabic linguist in the Army and used Anki, first at the start to ramp-up, and then later on to broaden my vocabulary, so I definitely think it is a good tool, but the 88 weeks of classes day-in, day-out with native speakers helped a lot more.
Anki (or diligent use of flashcards) is good for the vocab part of languages (and that's admittedly a big part of it), but the task of learning a language is much more holistic than people sometimes realize. They want to min/max, and I get that, but language is something innate in us so it's essential to realize how important immersion/interaction is.
I find Anki is useful for boosting the frequency of important but medium-frequency words/phrases.
This is where language learning usually plateaus. Assuming one is being constantly exposed to comprehensible input, the first 80% (by Pareto principle) is usually easy because they're high frequency patterns and the brain automatically picks up on what to pay attention to and tries to retain them. (pattern/word frequency)
But then there's the 10% of high-leverage phrases that native speakers use (which makes them sound native) but not quite often enough for our brains to pattern match. These are the hardest to retain because it's diminishing returns for our brains. (weak signals in training data)
This is where Anki helps: the SRS artificially boosts the signals for these phrases. (synthetic data)
I also use Anki for easy confused words/phrases -- in Portuguese, "rodoviária" (bus station) and "rodovia" (highway) are easily confused, but Anki's SRS prompts me to differentiate them. (discriminative learning)
I was an Arabic linguist in the Army and used Anki, first at the start to ramp-up, and then later on to broaden my vocabulary, so I definitely think it is a good tool, but the 88 weeks of classes day-in, day-out with native speakers helped a lot more.
Anki (or diligent use of flashcards) is good for the vocab part of languages (and that's admittedly a big part of it), but the task of learning a language is much more holistic than people sometimes realize. They want to min/max, and I get that, but language is something innate in us so it's essential to realize how important immersion/interaction is.