Linguistic "efficiency" is a very amorphous concept. While languages such as the Sino-Tibetan (Chinese, Burmese, et cetera) and Austro-Thai (Thai, Lao, Shan) languages' elegantly simple grammar makes them very easy to acquire, said simplicity can hinder precise communication. Conversely, more complicated grammatical structures are more difficult to master, but can offer greater scope for both precision and for artistry.
For example, in standard spoken Lao and Thai, verbs are almost never conjugated, nouns and pronouns are not declined, and the subject of a sentence is often omitted if it seems obvious. This makes learning Lao or Thai very simple, but means miscommunication is more likely, and its harder to jump into the middle of a conversation if you haven't been following it from the beginning.
I have picked up fairly decent Lao and Thai with no formal study or grammar book and only a dictionary to guide me, something I'm sure I could not do with a more grammatically complex language such as Russian or Korean. On the other hand, there are many an occasion where I stumble into a Lao/Thai conversation and know immediately what the verb is, but I do not know if said verb was a command or a statement; if a statement, I do not know if it refers to the past, present, or future; and, if the subject noun/pronoun was dropped, I have no idea if the speaker was referring to him/herself, myself, ourselves, or a third party. Context usually will clue one in, but not always.
A more complex grammar, such as English uses, is obviously more difficult to learn. As an English teacher, I have seen my students struggle to come to terms with subject/verb agreement, declining pronouns (I/me/my/myself), conjugating English's rather convoluted verb tenses, not to mention all the irregularities inherent in English.
English verb tenses in particular can be nasty. Even in languages that conjugate their verbs, there are rarely as many tenses. For example, Japanese and Korean use essentially:
- present (I do)
- present continuous (I am doing)
- preterite (I did)
- future (I will do)
- present perfect (I have done) - but only in the sense of experience, i.e. "I have done that before".
- past perfect (I had done)
In addition to these, English throws in:
- present perfect (I have done) - both experientially and as a current state, i.e. "I have done the dishes (and they are still clean)", as opposed to "I did the dishes (and they may or may not be dirty again)".
- future perfect (I will have done)
- imperfect (I used to do)
- past continuous (I was doing)
- future continuous (I will be doing)
- present perfect continuous (I have been doing)
- past perfect continuous (I had been doing)
- future perfect continuous(!) (I will have been doing)
- conditional (I would do; I would have done)
Such complexity is obviously difficult to learn, but it allows for greater precision and, coupled with the fact that English never drops a sentence's subject, allows any one coming late to the conversation to immediately discern a command from a statement, whether the subject is the speaker, the listener, or a third party, and when exactly the action has/is/will take place.
Taking the conjugation example even further, languages such as Korean and Japanese, while conjugating verbs for tense (past/present/future), also conjugate mood, feeling, and politeness. Thus, "I/You/We/They do" or "He/She/It does" can be:
- 해 hae (informal)
- 해요 haeyo (informal polite)
- 합니다 hamnida (formal)
- 하세요 haseyo (informal polite respectful)
- 하십니다 hashimnida (formal polite respectful)
- 하는데 haneundeh (softening a statement as when explaining or making an excuse)
- 하는데요 haneundeyo (as above, but more polite)
- 하차나 hachana (restating a known condition as in I do, you know).
- 하차나요 hachanayo (as above, but more polite)
- 하군요 hagunyo (mild emphasis)
- 하져 hajaw (confirmation as in "You do, don't you")
- 하지요 hachiyo (as above, but more polite)
- 하자 haja ("Let's go")
- 합시다 hapshida (as above, but polite)
There are more variations, but you get the picture. And this is only for the present tense. Throw in past and future tenses, commands, suggestions, offers, requests, et cetera, and conjugating a Korean verb makes conjugating a Latin verb seem like child's play. Again, the grammar is brutally complex to master, but allows any casual listener to know when the action in question took/takes/will take place, and some of the speaker's feelings/motives for relaying said information. The Korean (and Japanese) tendency to drop a sentence's subject does, however, detract from its precision, but allows for smoother casual verbal exchanges.
Which of the above is more efficient? Obviously, Thai or Lao if "efficiency" means the speed with which non-native speakers can learn the language. English, by not dropping its subjects, is most efficient for allowing a casual listener to automatically grasp who did what and when. Korean, with its innumerable inflexions, is probably more efficient at conveying the speaker's intent/feeling in making a given utterance.
Though a native English speaker, I have always tried to avoid any tendency towards linguistic chauvinism. The more non-English languages I learn, though, the more enamored I become with English. This has less to do with its "efficiency" than with its "flexibility and artistry", which is largely at odds with any sense of efficiency. Being the bastard product of Celtic/Roman/Saxon/Danish/French/Greek miscegenation, English, as an imperial language, then went out and absorbed words from literally dozens of other languages. Such a large and varied lexicon, while vastly complicating attempts to master it, provides it with the ability to mutate and reconstitute itself more quickly than any other language of which I am aware. Few other languages could give you a word such as "craptacular", splicing a genarally vulgar Germannic element, "crap", on to a more sophisticated Latin base, "spectacular", to produce a word whose meaning has changed little, but which conveys an entirely new sense of that meaning.
Another benefit of English's imperial past is the wide variety of Englishes on the planet. British, American, Australian English, and their sub-dialects (Geordies/Scousers/Downeasters/Ebonics), not to mention Indian English, Singaporean English, Kenyan, Ghanaian, Jamaican English, all add to the richness, if not the efficiency, of English that perhaps only French or Spanish could hope to match.
As for writing systems (an ENTIRELY different matter), ideogramic/logogramic languages have the advantage of allowing speakers of different languages to communicate in writing. Literate speakers of Mandarin, Cantonese, Hakka, et cetera, as well as educated Japanese, and long ago educated Koreans and Vietnamese, even if they had no common spoken tongue, could communicate on paper to a remarkable extent. Even now, if one wanted to, one could master Chinese characters in one's native tongue and communicate fully in writing while never learning to speak any Chinese dialect.
That said, within a single language area, an alphabetic writing system is more efficient in that it is easier to learn and more flexible for the introduction of new words into the lexicon. The Latin script used in Western European languages is a highly adaptive alphabet as evidenced by its ability to render such a diverse range of languages into writing, however imperfectly (explaining some of the ridiculous spellings one finds in English).
Korean 한글 (hangul) is perhaps the most efficient alphabet there is for its own language, but it lacks quite a few sounds vital to other languages (no "f", "th", "z"), can not replicate final aspirants (my name is "Greg" but my students call me "Greck), and has no provision for consonant clusters ("stripes" becomes 스트라이프스, prounounced "seu-teu-ra-ee-peu-seu).
Not all alphabets are created equal, though. The Latin and Korean scripts were at least created with simplicity in mind. The Thai script was design as a court/temple script and was intended to be as ornate as possible. There are, for example, five different letters that to a Westerner look exactly like the letter "W" except for the placement of a loop on the left-hand arm and the length of the right hand arm. Thus, even the slightest irregularity in writing style can significantly alter the pronuncuation and meaning of a word.
Japanese is an odd hybrid - syllabic, not alphabetic. In both katakana and hiragana, consonants can not be separated from their following vowel. Therefore, "stripes" pronounced as written in Japanese is "su-to-ra-ee-pu-su" (sorry, no katagana/hiragana on this machine). As such, no matter how well Japanese kana might fit Japanese, it would never do for accurately transcribing other languages.
All in all, 'efficiency" is too hard a concept to define in regard to languages. Adaptability and simplicity are probably more realistic goals. English, by dint of its polyglot history and imperfect but malleable alphabet, is probably the most adaptable. Of the simpler, grammatically-speaking at least, languages Mandarin Chinese is both the most widespread, and perhaps the most developed. Toss in the other colonial/imperial languages - French, Spanish, Arabic, Russian - plus Hindi/Urdu, and you have most of the world covered.
. (Eventhough some Japanese Kanji Characters are shared with Traditional Chinese Characters).
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and that I frequently get lost when translating my thoughts into a 1.5 page sentence 
