Which are the hardest languages to learn? The Foreign Service Institute ranks Thai as a Category IV “super-hard” language, requiring 1,100+ hours to reach proficiency. Spanish, rated “easy,” needs just 600 hours. Common sense says more people should finish Spanish than Thai, right?
Ling’s 2025 retention data tells a different story. We analyzed 3,891 learners across 78 languages and discovered something unexpected: the harder the language, the higher the retention rate. Hard languages (Category III-V) retained learners at significantly higher rates than easy languages (Category I-II)—suggesting that personal motivation matters far more than linguistic difficulty.
Key Research Findings:
– Hard languages (FSI Category III-V): 63.69% retention
– Easy languages (FSI Category I-II): 55.87% retention
– Hard languages show 14% higher retention than easy languages
– Lithuanian leads at 74.85% retention (Category IV, 167 learners)
– Four of top five retention languages are Category IV-V (“hard/super-hard”)
– Thai (65.21%) outperforms Malay (56.04%) despite requiring 2x study hours
Data source: Ling app internal analytics, 3,891 learners, January-December 2025
What Makes A Language “Hard” To Learn?
The Foreign Service Institute (FSI) has spent decades measuring language difficulty for English speakers. Their rankings aren’t subjective, they’re based on thousands of hours of classroom data tracking how long it takes diplomats and intelligence officers to reach professional proficiency.
FSI Difficulty Categories Explained
Category I (Easy): 24-30 weeks (600-750 hours)
These are the languages with straightforward grammar and familiar vocabulary for English speakers. Spanish, French, Italian, Portuguese, and other Romance languages fall here. Shared Latin roots mean you already recognize thousands of words before you start.
Category II (Moderate): 30 weeks (750 hours)
Languages that haveslightly more grammatical complexity fall in this category. German sits here with its four cases and compound words, along with Indonesian, Malay, and Swahili.
Category III (Moderate-Hard): 36 weeks (900 hours)
This category is forlanguages with different writing systems or unfamiliar grammatical structures. Eastern European languages like Czech, Albanian, as well as Southeast Asian Khmer require more study time.
Category IV (Hard): 44 weeks (1,100 hours)
These languages have significant linguistic distance from English. Thai, Vietnamese, Russian, Finnish, Turkish, Hungarian, and Serbian demand substantially more effort. New scripts, tonal systems, extensive case systems, or verb conjugations create steep learning curves.
Category V (Super-Hard): 88 weeks (2,200 hours)
The most challenging languages for English speakers fall under this category. Arabic, Cantonese, Mandarin, Japanese, and Korean require double the study time of Category IV languages. Complex writing systems (thousands of characters), tonal pronunciation, and grammatical structures with no English parallels explain the difficulty.
These rankings measure linguistic distance from English: phonology, grammar, vocabulary, and writing systems. The further a language sits from English, the more hours learners need to achieve proficiency.
The Twist: Ling’s Retention Data Contradicts Difficulty Rankings
We analyzed retention rates for learners who completed their first lesson in each language between January and December 2025. The question: how many returned after one day, seven days, and 30 days?
The results surprised us!
30-Day Retention: Hard Vs Easy Languages
| Language Category | Average D30 Retention | Sample |
| Category III-V (Hard/Super-Hard) | 63.69% | 8 languages |
| Category I-II (Easy/Moderate) | 55.87% | 2 languages |
Hard languages have 14% higher retention among Ling users than easy languages.
Top 5 Languages By 30-Day Retention
| Rank | Language | FSI Category | D30 Retention | Sample Size |
| 1 | Lithuanian | IV (Hard) | 74.85% | 167 users |
| 2 | Khmer | III (Moderate) | 71.43% | 168 users |
| 3 | Serbian | IV (Hard) | 69.41% | 376 users |
| 4 | Cantonese | V (Super-Hard) | 68.50% | 200 users |
| 5 | Thai | IV (Hard) | 65.21% | 1,788 users |
Four of the top five retention languages are Category IV or V, officially classified as “hard” or “super-hard.”
Malay, a Category II language, shows 56.04% retention. Korean and Japanese, both Category V “super-hard” languages, show 47.78% and 51.03%, respectively. But Serbian, Lithuanian, Khmer, Cantonese, and Thai all exceed 60% retention despite their difficulty.
Among Ling app users in 2025, languages classified as “hard” by FSI showed 63.69% retention compared to 55.87% for “easy” languages—a 14% higher persistence rate despite requiring 3x more study hours.
Ling app 2025 Retention Data Analysis.
Language Retention: What’s Driving This Pattern?
Retention rates in the Ling app reveal something FSI classroom hours can’t measure: personal motivation matters more than linguistic difficulty.
Why Thai Shows 65% Retention Despite Being “Hard”
Thailand welcomed over 32 million tourists in 2024. Many of them relocate. Digital nomad visas, affordable living costs, and vibrant expat communities mean people build lives in Thailand. Learning Thai stops being theoretical when you need it to ask your landlord about repairs, navigate healthcare, or chat with neighbors.
Additionally, Thai has five tones. Pitch changes meaning entirely: “ma” can mean horse, dog, come, mother, or function as a question particle depending on tone.
That’s why native speaker audio helps learners hear and reproduce tones accurately, removing the intimidation factor. Apps that provide authentic pronunciation from real speakers are essential for tonal languages.
Thai learners in the Ling app aren’t casual learners. They have Thai partners, they plan extended stays in Thailand, or are deeply appreciative of Thai culture. That emotional investment transforms tonal pronunciation from frustrating to essential. When understanding your partner’s family depends on getting tones right, you practice until you do.
Serbian: Heritage Connection Drives Persistence Through Seven Cases
Serbian ranks Category IV for good reason: seven grammatical cases, verb aspects, and Cyrillic script create genuine challenges. Yet Serbian learners in the Ling app show 69.41% retention, outperforming easier alternatives.
Geographic data from 2025 confirms why: Serbian learners are concentrated in Serbia itself, with significant communities in Russia and neighboring Montenegro. They’re people reconnecting with Serbian heritage, living in Belgrade, or maintaining family connections.
Heritage learners don’t just memorize case endings. They practice conversations with grandparents, try to understand family history, and access cultural identity. Learning about ‘declining adjectives’ in seven cases feels meaningful when it lets you read letters from relatives or follow family conversations on the dinner table.
Lithuanian: Small But Exceptional
Lithuanian, another Category IV language with seven cases and pitch accent, tops retention rankings. The sample size (167 users) suggests a small but exceptionally committed community of learners.
Lithuanian attracts heritage speakers reconnecting with Baltic roots as well as expats in Vilnius. Lithuanian being one of Europe’s oldest languages with distinct phonology and grammar, Lithuanian learners are typically passionate about the language itself, not just seeking an “easy” option.
Eastern European Languages: Small But Committed Communities
Albanian learners show 61.33% retention despite the language’s Category III moderate difficulty. Ling’s Geographic data from 2025 reveals diaspora patterns: Germany leads with 584 Albanian learners, followed by Italy (330) and Switzerland (153). reflecting communities where second and third-generation immigrants reconnect with their heritage language.
Only 220 Albanian learners are based in Albania itself. The majority study from diaspora hubs, maintaining linguistic ties across generations. This creates learner communities with deep personal stakes, like understanding grandparents, participating in family gatherings, and preserving cultural identity.
What does this reflect? Scarcity of learning resources paradoxically increases commitment. When only one or two quality apps teach Albanian, learners can’t endlessly switch resources during difficult chapters. They commit to what works and persist through challenges.
Asian Languages: Cultural Motivation Drives Persistence
Korean: K-Pop And K-Drama Create Global Learners
Korean shows lower retention than other hard languages but still significant given its Category V super-hard status. K-pop and K-dramas created unprecedented global motivation to learn Korean that transcends linguistic difficulty.
K-pop fans don’t want English translations of lyrics, they want direct understanding of what artists express. K-drama viewers tire of subtitles as they miss wordplay and cultural nuances. Korean learning resources that offer cultural immersion creates learners genuinely invested in Korean’s honorific system and sentence-final particles.
Furthermore, Hangul, Korea’s writing system, offers early momentum. Unlike Chinese characters or Thai script, Hangul can be learned in days. That quick victory, reading Korean signs and social media before understanding the words, builds confidence for tackling harder grammar later.
Cantonese: Cultural Preservation For Diaspora Communities
Cantonese ranks Category V with good reason: nine tones, no alphabet, and thousands of characters to memorize. Yet Cantonese learners show strong retention in the Ling app, fourth highest overall.
Heritage speakers form the core of Cantonese learners. While Mandarin dominates mainland China and official contexts in Hong Kong, Cantonese represents cultural preservation for diaspora communities.
Learning Cantonese connects heritage speakers to grandparents, regional identity, and linguistic traditions threatened by Mandarin’s spread.
Interactive native speaker audio in Ling ensures learners hear authentic pronunciation from real speakers, essential for distinguishing nine different tones. For tonal languages, hearing native speakers produce sounds in natural speech contexts isn’t optional, it’s foundational.
Filipino: Heritage Learners Drive The Second-Largest User Base
Filipino shows moderate retention in the Ling app. The Philippines has over 10 million overseas workers globally, creating massive demand for family members, partners, and children of Filipino immigrants to learn the language.
Filipino learners in the Ling app (1,154 daily active users, second-highest) study to understand grandparents, connect with extended family, and maintain ties to Filipino culture. This heritage motivation sustains learners through Filipino’s verb-focus system and Tagalog grammar.
Filipino’s borrowings from Spanish and English create familiarity: kumusta (¿cómo está?), silya (silla = chair), bintana (ventana = window). This vocabulary recognition provides footholds but doesn’t guarantee completion. In such cases, personal connection matters more than linguistic ease.
Why “Hard” Languages Outperform “Easy” Ones
FSI Measures Classroom Hours, Not Personal Stakes
The FSI difficulty rankings accurately predict classroom instruction time under ideal conditions: motivated adult learners, experienced instructors, structured curriculum, peer accountability, and professional necessity (diplomatic postings, intelligence work).
Real-world language learning looks different. Most people study independently through apps, fragmented practice (15 minutes here, 30 minutes there), without peer pressure or professional requirements. In this context, linguistic difficulty predicts required study hours but not dropout rates.
Motivation Creates Persistence Through Challenges
A Thai learner working through five tones and unfamiliar script isn’t comparing progress to FSI estimates. They’re measuring success by whether they can order food in Thai tomorrow, participate in their Thai partner’s family dinner conversation next week, or navigate Bangkok independently next month.
Personal connection to a language,through heritage, relationships, residence, or deep cultural interest, drives completion rates significantly higher than linguistic simplicity alone. This effect transforms difficulty from an obstacle into a meaningful challenge.
A Serbian heritage learner persists through seven cases while a casual French learner abandons irregular verbs. The Serbian learner has compelling reasons (family, identity, belonging). The French learner might have chosen French because someone said it was “easy.”
Specialization Creates Commitment
Ling teaches over 70 languages with a focus on underserved Asian and Eastern European languages. Learners who choose Ling specifically sought tools for Thai, Serbian, Albanian, Lithuanian, Khmer, or Georgian, languages with limited learning resources elsewhere.
This creates self-selection bias, but that’s precisely the point. Someone downloading Ling for Thai already has Thai in their life: a partner, relocation plans, extended travel, or cultural passion. They’re not experimenting with language learning as a hobby. They’re committed to Thai specifically.
The app’s native speaker audio, cultural explanations, and gamified 10-15 minute lessons create sustainable habits. But the fundamental driver is motivation. Ling’s specialization attracts learners with personal stakes, and personal stakes predict persistence better than difficulty ratings.
Which “Hard” Languages Have The Best Resources?
Not all hard languages offer equal learning support. Some have extensive resources while others remain underserved despite their difficulty.
Well-Supported Hard Languages
Mandarin Chinese (Cat. V): Massive learner demand means abundant apps, textbooks, tutors, and media. Despite being super-hard, resources make independent study feasible.
Japanese (Cat. V): Anime, manga, and cultural interest created extensive learning materials. Multiple writing systems remain challenging, but support exists.
Korean (Cat. V): The Korean Wave sparked global interest, generating quality learning apps, structured courses, and accessible media for practice.
Arabic (Cat. V): Religious significance and geopolitical importance created robust learning infrastructure despite dialectal complexity.
Underserved Hard Languages (Ling’s Specialization)
Thai (Cat. IV): Limited quality apps despite tourism. Ling fills a gap for learners needing practical Thai.
Serbian (Cat. IV): Few mainstream apps teach Serbian. Heritage learners and expats have limited options.
Albanian (Cat. III): Diaspora demand but minimal learning resources. Ling serves Albanian communities globally.
Lithuanian (Cat. IV): Extremely limited resources. Ling’s Lithuanian course serves a small but dedicated community.
Khmer (Cat. III): Underdeveloped learning materials despite Cambodia’s growing tourism and development sector.
This scarcity creates the commitment pattern visible in Ling’s data. When learners can’t switch between dozens of apps, they commit to what works and persist through difficulty.
Do Difficulty Rankings Still Matter When It Comes To Learning A Language?
FSI rankings aren’t wrong. Category V languages genuinely require more study hours than Category I languages. Thai grammar and tones demand more time than Spanish grammar and pronunciation. The rankings accurately measure linguistic distance from English.
But for independent learners, difficulty rankings predict study requirements, not completion likelihood. Motivation predicts completion. Choose a language connected to your life, heritage, relationships, or passions, and difficulty becomes a challenge to overcome rather than a reason to quit.
The “hardest” language to finish is the one you don’t care about. On the other hand, grammar complexity, unfamiliar sounds, and difficult scripts become manageable obstacles when you have compelling reasons to persist. The easiest language to finish is the one woven into your life, regardless of FSI category.
FAQs About Learning “Hard” Languages
What Is The Hardest Language To Learn For English Speakers?
According to the Foreign Service Institute, Category V languages (Arabic, Cantonese, Mandarin, Japanese, Korean) are the toughest languages in the world, requiring 2,200 hours versus 600 hours for Category I languages. However, Ling’s retention data shows learners stick with hard languages at higher rates when they have personal motivation. Cantonese shows 68.5% retention despite nine tones and thousands of characters.
Why Do Hard Languages Have Higher Retention In The Ling App?
Learners studying hard languages typically have stronger personal motivations: heritage connections, relationships, residence in the country, or deep cultural interest. These compelling reasons sustain persistence through challenges. Serbian learners (69% retention) often reconnect with family roots. Thai learners (65% retention) frequently have Thai partners or live in Thailand.
Should I Avoid Hard Languages As A Beginner?
No. Choose languages you’ll actually use. Living in Korea makes Korean more practical than Spanish, despite Spanish being linguistically easier. Family connections, work requirements, or cultural passion create motivation that matters more than difficulty ratings. The language you’ll finish is the one connected to your real life.
How Long Does It Take To Learn A Category IV Or V Language?
FSI estimates suggest 1,100 hours for Category IV and 2,200 hours for Category V languages in intensive classroom settings. Independent learners who use apps for learning a language progress differently. Consistent daily practice (15-30 minutes) builds conversational competence faster than sporadic intensive sessions. Personal stakes keep learners engaged long-term.
Can You Really Learn Tonal Languages Through An App?
App-based learning works well for tonal languages when it includes interactive native speaker audio throughout lessons. Native speaker audio in Ling ensures learners hear authentic pronunciation from real speakers, essential for distinguishing and producing tones accurately. Learners need to hear tones in context repeatedly, not just read descriptions.
What’s The Hardest Part Of Learning Thai, Korean, Or Serbian?
Thai’s five tones challenge most learners initially. Pitch changes meaning entirely, requiring extensive listening practice. Korean’s honorific system demands understanding social context and formality levels before speaking. Serbian’s seven cases require memorizing different noun endings for grammatical function. However, committed learners report these challenges become manageable with consistent practice and personal motivation.
Why Do Eastern European Languages Show High Retention In Ling?
Eastern European languages attract heritage learners reconnecting with family roots, expats needing the language for daily life, and language enthusiasts drawn to underserved languages. Serbian, Albanian, and Lithuanian learners often have personal stakes (family, identity, residence) that sustain them through grammatical complexity. Limited alternative resources also increase commitment.
Which Is Harder: Thai Or Spanish?
Thai (Category IV) requires nearly double the study hours of Spanish (Category I) according to FSI rankings. Thai’s tonal system, script, and grammar create genuine difficulty. However, Ling’s data shows Thai learners (65% retention) persist at higher rates than learners of easier languages. Personal motivation determines completion more than linguistic difficulty.
How Does Ling Help With Difficult Languages?
Ling teaches over 60 languages with a focus on underserved Asian and Eastern European languages, combining native speaker audio, cultural context, and gamified 10-15 minute lessons. This approach builds sustainable daily habits. Practical conversational content creates quick wins (ordering food, basic greetings) that maintain momentum through harder grammar challenges later.
Does Learning A Hard Language First Make Easy Languages Easier?
Learning a hard language builds metalinguistic awareness and study habits that transfer to easier languages. Someone who masters Thai tones or Serbian cases has proven they can handle linguistic complexity. However, motivation matters most. Choose your first language based on personal connection, not strategic difficulty sequencing.
Start Learning The Language That Matters To You
Ling’s 2025 retention data reveals a truth that contradicts common language learning advice: difficulty doesn’t predict whether you’ll finish learning a language. Personal connection does.
Lithuanian, Khmer, Serbian, Cantonese, and Thai—languages officially classified as “moderate-hard” to “super-hard”—show the highest retention rates in the Ling app. They outperform linguistically easier alternatives because learners have compelling reasons to persist.
Whether you’re moving to Thailand, reconnecting with Serbian heritage, or passionate about Korean culture, that personal stake transforms challenges into meaningful milestones. Tonal pronunciation stops feeling tedious when it means understanding your Thai partner’s family. Serbian case endings stop feeling arbitrary when they unlock conversations with grandparents.
The “hardest” language to finish is the one you don’t care about, regardless of how easy linguists rate it. The language you’ll actually finish is the one woven into your life: where you’re going, who you love, where you come from, or what culture captivates you.
Ready to start a language you’ll actually finish? Choose the language connected to your real life. The grammar will follow.
Research Methodology: This analysis examined 30-day retention rates for 3,891 language learners in the Ling app who completed their first lesson between January 1-December 31, 2025. Retention data was tracked via Ling’s internal analytics platform. Languages were classified using Foreign Service Institute difficulty categories (I-V). Geographic distribution data reflects all active Ling app users in 2025.
