Yes, you can learn some important aspects of a foreign language, BUT achieving full fluency requires a lot more than just an app.
Software like Duolingo, Babbel, Anki, or LingQ are very popular and can be useful tools in some ways  but they can only really help with formal vocabulary, grammar, and basic sentence structure. Unfortunately, and typically, once away from the safety of those apps you will quickly forget most of what you have learned and find yourself unable to maintain a real conversation!
Fluency requires real-life practice and human interaction.

What Apps Can Help With

✅ Learning a basic vocabulary
✅ Learning some formal grammar rules
✅ Practicing reading and listening
✅ Forming simple sentences

What Apps Can’t Do Alone

❌ Develop deep conversational skills – You need real interaction for this.
❌ Perfect pronunciation – Speech AI can help, but native speakers are always far better.
❌ Teach cultural nuances – Language is deeply tied to culture and apps do not really cover those vital areas.
❌ Help you think in the language – That comes from practice out loud, immersion and practical, real-life use.