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The course starts at the alphabet — 22 units before A1 even begins, in all four languages.
A fair comparison
Lingua Doctor vs Duolingo
Independent comparison. Lingua Doctor is not affiliated with, or endorsed by, Duolingo. Figures about Lingua Doctor are counted from the shipped course; figures about Duolingo come from public sources and change.
Choose Lingua Doctor when…
You want explanations in your own language
Arabic, Turkish, German and English are each both a course and an explanation language.
You want to know what you actually know
Every unit maps to explicit CEFR objectives, and only independent correct production counts toward your level.
Choose Duolingo when…
You want a very large catalogue
Duolingo offers dozens of languages. This app offers four, and will for some time.
You want hundreds of hours in one app
The course here is about 76 hours of authored material. Duolingo is far larger.
You want instant marking offline
Both apps let you study offline — you can save a unit, audio included, before you lose signal. The difference is marking: Duolingo checks your answers on the spot, while here they are recorded offline and marked when you reconnect, because only the server holds the answer key.
The honest verdict
Lingua Doctor is narrower and earlier. Its real advantage is the alphabet-first path, mother-tongue explanations, and progress that only counts when you produce the language yourself. It is not a claim to have more content — today, it plainly has less.