How long does it take to learn a language?

What's the number of hours necessary to learn a language up to a certain level? Before we answer the first question we have to ask (and answer) two more questions. What level of proficiency are we talking (or writing) about and who's asking?

The Interagency Language Roundtable (ILR) scale is a set of descriptions of abilities to communicate in a language. It was originally developed by the Interagency Language Roundtable which included the United States Foreign Service Institute. It describes five levels of language proficiency. One big caveat is that this scale was developed with English language speakers in mind. A native speaker of an Indo-European language with a certain level of language learning experience may try adapting it to his needs. The five levels on the ILR scale:

1 Elementary proficiency
2 Limited Working proficiency
3 Professional Working proficiency
4 Full Professional proficiency
5 Native or Bilingual proficiency

The scale can be fine-tuned to a range from 0 and 0+, 1, 1+ etc to 5. Level 5 is that of an educated native speaker of the target language (a bit of a murky concept nowadays).

Level 1 to 1+ is about “most survival needs and limited social demands.”

Level 2 is about routine social demands and limited/routine work requirements. Level 2+ would require some ability to communicate on concrete topics.

Level 3-3+ is about being able to speak with sufficient structural accuracy and having a sufficient vocabulary to participate effectively in most formal and informal conversations. Few courses would be able to take you any further. From this point on, you’re on your own, the language will either progress or deteriorate. Use it or lose it.

Level 4 A speaker would possess a great deal of fluency, and be able to employ grammatical constructs, vocabulary and idiomatic expressions with accuracy.

Level 5 is about complete fluency, rich vocabulary and competent use of and idioms, cultural references and colloquialisms.

Each level is progressively more time consuming. All 5 levels measure independently speaking, listening and reading skills.

American Council for the Teaching of Foreign Languages (ACTFL) scale is compatible with the FSI scale and assesses all four language skills. The Common European Framework of Reference for Languages: Learning, Teaching, Assessment, or CEFR scale is a somewhat wordy name for a scale designed to help teachers assess and validate all four language skills. The UNIcert scale is based on the CEFR scale for university accreditation purposes.

Learning expectations – number of study hours needed to achieve level 3 proficiency in speaking and reading: General Professional Proficiency in Speaking (S3) and General Professional Proficiency in Reading (R3) according to the ILR scale. I have loosely lumped languages together for easy reading according to linguistic, geographic criteria. Languages marked by an asterisk are considered somewhat more difficult than other languages in the same group.

This is a RELATIVE language difficulty list. A more optimistic and correct name would be "approximate learning time" or "approximate learning expectation" list.

The most commonly used language difficulty scale is the one developed by the Foreign Service Institute (The "FSI scale").

The Defense Language Institute (DLI) has developed a separate foreign language difficulty scale (the "DLI scale") based on language relationships and "practical experience". The DLI scale has four categories.

The FSI scale

Group I (24 weeks) Approximately 575-600 hours

Dutch
French
Italian
Portuguese
Romanian
Scandinavian languages
Spanish

German is between the two groups as it requires 750 hours

Group II (30 weeks) Approximately 1100 hours
Albanian
Amharic
Armenian, Azerbaijani, *Georgian
Slavic languages
Greek
Hebrew
Hindi (all Indian languages belonging to the Indo-European branch)
*Hungarian, Finnish
Khmer, Lao, *Vietnamese, *Thai ,Burmese
Baltic languages
*Mongolian
Persian (Dari, Farsi, Tajik)
Tagalog
Turkish, Uzbek
Xhosa, Zulu

Group III (44 weeks) Approximately 2200 hours. Usual description for this group is “exceptionally difficult” for native English speakers.

Arabic
Cantonese
Mandarin
*Japanese
Korean

Please note that the three groups reflect experiences of motivated adult students with some previous knowledge of foreign languages in a class setting. The FSI students are described as having a "good aptitude for formal language study, plus knowledge of several other foreign languages". Their schedule calls for 25 hours of class per week with 3-4 hours per day of directed self-study. Accounting for self-study, the student needs approximately...

Category I: 1,100 HOURS

Category II: 2000 HOURS

Category III: 4000 HOURS

... to reach level 3 on the ILR proficiency scale (professional working proficiency) in speaking, listening and reading.

What about the CEFR scale? The DELF (“Diplôme d’Etudes en Langue Française”) and DALF (“Diplôme Approfondi de Langue Française”) consists of 6 diplomas independent from each other. They correspond to the 6 levels of the Common European Framework of References for languages.

Each DELF / DALF exam corresponds to the following hours of teaching :
DELF A1 :   60 hours from Beginner level
DELF A2 : 160 hours from Beginner level (100 hours from DELF A1)
DELF B1 : 310 hours from Beginner level (150 hours from DELF A2)
DELF B2 : 490 hours from Beginner level (180 hours from DELF B1)
DALF C1 : 690 hours from Beginner level (200 hours from DELF B2)
DALF C2 : 890 hours from Beginner level (200 hours from DALF C1)

Another description is also current:

Levels A1 and A2: Elementary Levels
DELF A1 (from 60 to 100 hours of French)
DELF A2 (about 200 hours of French)

Levels B1 and B2: Independent Levels
DELF B1 (about 400 hours of French)
DELF B2 (about 600 hours of French)

Levels C1 and C2: Experienced Levels
DALF C1 (about 800 hours of French)
DALF C2 (900 hours or more of French)