Here is some interesting information about language proficiency, which I took from the Interagency Langauge Roundtable, at http://www.govtilr.org/
S-0 NO PROFICIENCY
Unable to function in the spoken language. Oral production is limited to occasional isolated words. Has essentially no communicative ability.
S-0+ MEMORIZED PROFICIENCY
Able to satisfy immediate needs using rehearsed utterances. Shows little real autonomy of expression, flexibility, or spontaneity. Can ask questions or make statements with reasonable accuracy only with memorized utterances or formulae. Attempts at creating speech are usually unsuccessful.
Examples: The S-0+'s vocabulary is usually limited to areas of immediate survival needs. Most utterances are telegraphic; that is, functors (linking words, markers, and the like) are omitted, confused, or distorted. An S-0+ can usually differentiate most significant sounds when produced in isolation, but, when combined in words or groups of words, errors may be frequent. Even with repetition, communication is severely limited even with persons used to dealing with foreigners. Stress, intonation, tone, etc. are usually quite faulty.
S-1 ELEMENTARY PROFICIENCY
Able to satisfy minimum courtesy requirements and maintain very simple face-to-face conversations on familiar topics. A native speaker must often use slowed speech, repetition, paraphrase, or a combination of these to be understood by an S-1. Similarly, the native speaker must strain and employ real-world knowledge to understand even simple statements/questions from the S-1. An S-1 speaker has a functional, but limited proficiency. Misunderstandings are frequent, but the S-1 is able to ask for help and to verify comprehension of native speech in face-to-face interaction. The S-1 is unable to produce continuous discourse except with rehearsed material.
Examples: Structural accuracy is likely to be random or severely limited. Time concepts are vague. Vocabulary is inaccurate, and its range is very narrow. The S-1 often speaks with great difficulty. By repeating, such speakers can make themselves understood to native speakers who are in regular contact with foreigners but there is little precision in the information conveyed. Needs, experience, or training may vary greatly from individual to individual; for example, S-1s may have encountered quite different vocabulary areas. However, the S-1 can typically satisfy predictable, simple, personal and accommodation needs; can generally meet courtesy, introduction, and identification requirements; exchange greetings; elicit and provide, for example, predictable and skeletal biographical information. An S-1 might give information about business hours, explain routine procedures in a limited way, and state in a simple manner what actions will be taken. The S-1 is able to formulate some questions even in languages with complicated question constructions. Almost every utterance may be characterized by structural errors and errors in basic grammatical relations. Vocabulary is extremely limited and characteristically does not include modifiers. Pronunciation, stress, and intonation are generally poor, often heavily influenced by another language. Use of structure and vocabulary is highly imprecise.
S-1+ ELEMENTARY PROFICIENCY, PLUS
Can initiate and maintain predictable face-to-face conversation and satisfy limited social demands. The S-1+ may, however, have little understanding of the social conventions of conversation. The interlocutor is generally required to strain and employ real-world knowledge to understand even some simple speech. An S-1+ may hesitate and may have to change subjects due to lack of language resources. Range and control of the language are limited. Speech largely consists of a series of short, discrete utterances.
Examples: An S-1+ is able to satisfy most travel and accommodation needs and a limited range of social demands beyond exchanges of skeletal biographic information. Speaking ability may extend beyond immediate survival needs. Accuracy in basic grammatical relations is evident, although not consistent. May exhibit the commoner forms of verb tenses, for example, but may make frequent errors in formation and selection. While some structures are established, errors occur in more complex patterns. The S-1+ typically cannot sustain coherent structures in longer utterances or unfamiliar situations. Ability to describe and give precise information is limited. Person, space, and time references are often used incorrectly. Pronunciation is understandable to natives used to dealing with foreigners. Can combine most significant sounds with reasonable comprehensibility, but has difficulty in producing certain sounds in certain positions or in certain combinations. Speech will usually be labored. Frequently has to repeat utterances to be understood by the general public.
S-2 LIMITED WORKING PROFICIENCY
Able to satisfy routine social demands and limited work requirements. Can handle routine work-related interactions that are limited in scope. In more complex and sophisticated work-related tasks, language usage generally disturbs the native speaker. Can handle with confidence, but not with facility, most normal high-frequency social conversational situations including extensive, but casual, conversations about current events, as well as work, family, and autobiographical information. The S-2 can get the gist of most everyday conversations but has some difficulty understanding native speakers in situations that require specialized or sophisticated knowledge. The S-2's utterances are minimally cohesive. Linguistic structure is usually not very elaborate and not thoroughly controlled; errors are frequent. Vocabulary use is appropriate for high-frequency utterances, but unusual or imprecise elsewhere.
Examples: While these interactions will vary widely from individual to individual, an S-2 can typically ask and answer predictable questions in the workplace and give straightforward instructions to subordinates. Additionally, the S-2 can participate in personal and accommodation-type interactions with elaboration and facility; that is, can give and understand complicated, detailed, and extensive directions and make non-routine changes in travel and accommodation arrangements. Simple structures and basic grammatical relations are typically controlled; however, there are areas of weakness. In the commonly taught languages, these may be simple markings such as plurals, articles, linking words, and negatives or more complex structures such as tense/aspect usage, case morphology, passive constructions, word order, and embedding.
S-2+ LIMITED WORKING PROFICIENCY, PLUS
Able to satisfy most work requirements with language usage that is often, but not always, acceptable and effective. An S-2+ shows considerable ability to communicative effectively on topics relating to particular interests and special fields of competence. Often shows a high degree of fluency and ease of speech, yet when under tension or pressure, the ability to use the language effectively may deteriorate. Comprehension of normal native speech is typically nearly complete. An S-2+ may miss cultural and local references and may require a native speaker to adjust to his/her limitations in some ways. Native speakers often perceive the S-2+'s speech to contain awkward or inaccurate phrasing of ideas, mistaken time, space, and person references, or to be in some way inappropriate, if not strictly incorrect.
Examples: Typically an S-2+ can participate in most social, formal, and informal interactions; but limitations either in range of contexts, types of tasks, or level of accuracy hinder effectiveness. The S-2+ may be ill at ease with the use of the language either in social interaction or in speaking at length in professional contexts. An S-2+ is generally strong in either structural precision or vocabulary, but not in both. Weakness or unevenness in one of the foregoing, or in pronunciation, occasionally results in miscommunication. Normally controls but cannot always easily produce general vocabulary. Discourse is often incohesive.
S-3 GENERAL PROFESSIONAL PROFICIENCY
Able to speak the language with sufficient structural accuracy and vocabulary to participate effectively in most formal and informal conversations on practical, social, and professional topics. Nevertheless, an S-3's limitations generally restrict the professional contexts of language use to matters of shared knowledge and/or international convention. Discourse is cohesive. An S-3 uses the language acceptably, but with some noticeable imperfections; yet, errors virtually never interfere with understanding and rarely disturb the native speaker. An S-3 can effectively combine structure and vocabulary to convey his/her meaning accurately. An S-3 speaks readily and fills pauses suitably. In face-to-face conversation with natives speaking the standard dialect at a normal rate of speech, comprehension is quite complete. Although cultural references, proverbs, and the implications of nuances and idiom may not be fully understood, the S-3 can easily repair the conversation. Pronunciation may be obviously foreign. Individual sounds are accurate; but stress, intonation, and pitch control may be faulty.
Examples: Can typically discuss particular interests and special fields of competence with reasonable ease. Can use the language as part of normal professional duties such as answering objections, clarifying points, justifying decisions, understanding the essence of challenges, stating and defending policy, conducting meetings, delivering briefings, or other extended, elaborate and informative monologues. Can reliably elicit information and informed opinion from native speakers. Structural inaccuracy is rarely the major cause of misunderstanding. Use of structural devices is flexible and elaborate. Without searching for words or phrases, an S-3 uses the language clearly and relatively naturally to elaborate concepts freely and make ideas easily understandable to native speakers. Errors occur in low-frequency and highly complex structures.
S-3+ GENERAL PROFESSIONAL PROFICIENCY, PLUS
Is often able to use the language to satisfy professional needs in a wide range of sophisticated and demanding tasks.
Examples: Despite obvious strengths, may exhibit some hesitancy, uncertainty, effort, or errors which limit the range of language-use tasks that can be reliably performed. Typically there is particular strength in fluency and one or more, but not all, of the following: has breadth of lexicon, including low- and medium-frequency items, especially socio-linguistic/cultural references and nuances of close synonyms; employs structural precision with sophisticated features that are readily, accurately, and appropriately controlled (such as complex modification and embedding in Indo-European languages); has discourse competence in a wide range of contexts and tasks, often matching a native speaker's strategic and organizational abilities and expectations. Occasional patterned errors occur in low frequency and highly complex structures.
S-4 ADVANCED PROFESSIONAL PROFICIENCY
Able to use the language fluently and accurately on all levels normally pertinent to professional needs. An S-4's language usage and ability to function are fully successful. Organizes discourse well, employing functional rhetorical speech devices, native cultural references, and understanding. Language ability only rarely hinders him/her in performing any task requiring language; yet, an S-4 would seldom be perceived as a native. Speaks effortlessly and smoothly and is able to use the language with a high degree of effectiveness, reliability, and precision for all representational purposes within the range of personal and professional experience and scope of responsibilities. Can serve as an informal interpreter in a range of unpredictable circumstances. Can perform extensive, sophisticated language tasks, encompassing most matters of interest to well-educated native speakers, including tasks that do not bear directly on a professional specialty.
Examples: Can discuss in detail concepts that are fundamentally different from those of the target culture and make those concepts clear and accessible to the native speaker. Similarly, an S-4 can understand the details and ramifications of concepts that are culturally or conceptually different form his/her own. Can set the tone of interpersonal official, semi-official, and non-professional verbal exchanges with a representative range of native speakers (in a range of varied audiences, purposes, tasks, and settings). Can play an effective role among native speakers in such contexts as conferences, lectures and debates on matters of disagreement. Can advocate a position at length, both formally and in chance encounters, using sophisticated verbal strategies. Can understand and reliably produce shifts of both subject matter and tone. Can understand native speakers of the standard and other major dialects in essentially any face-to-face interaction.
S-4+ ADVANCED PROFESSIONAL PROFICIENCY, PLUS
Speaking proficiency is regularly superior in all respects, usually equivalent to that of a well-educated, highly articulate native speaker. Language ability does not impede the performance of any language-use task. However, an S-4+ would not necessarily be perceived as culturally native.
Examples: An S-4+ organizes discourse well, employing functional rhetorical speech devices, native cultural references and understanding. Effectively applies a native speaker's social and circumstantial knowledge. However, cannot sustain that performance under all circumstances. While an S-4+ has a wide range and control of structure, an occasional non-native slip may occur. An S-4+ has a sophisticated control of vocabulary and phrasing that is rarely imprecise, yet there are occasional weaknesses in idioms, colloquialisms, pronunciation, cultural reference or there may be an occasional failure to interact in a totally native manner.
S-5 FUNCTIONALLY NATIVE PROFICIENCY
Speaking proficiency is functionally equivalent to that of a highly articulate, well-educated native speaker and reflects the cultural standards of the country where the language is natively spoken. An S-5 uses the language with complete flexibility and intuition, so that speech on all levels is fully accepted by well-educated native speakers in all of its features, including breadth of vocabulary and idiom, colloquialisms, and pertinent cultural references. Pronunciation is typically consistent with that of well-educated native speakers of a non-stigmatized dialect.