Hi again, everybody!
If extraterrestrial aliens genuinely visit Earth, it is obviously possible in principle that they may be able to learn to use contemporary human languages, and indeed it is frequently reported that aliens have been able to learn and use the languages known by the witnesses, or other human languages ancient or modern. For example, Marc Tolosano reports a (single-witness) case where ‘ufonauts’ allegedly encountered in 1983 in France spoke French fluently (and claimed that their species was familiar with all human languages).
There is a sub-set of cases of this general nature which involve alleged contemporary extraterrestrial knowledge of unexpected human languages, notably ancient languages such as Latin and Greek. M.H. Edwards (see earlier) discusses several cases of this kind. Obviously, one possible explanation for such ability (if genuine) involves visits to Earth in ancient times and the subsequent transmission of the knowledge acquired at that time (or the retention of the knowledge by aliens with very long life-spans).
John Dean reports contact with aliens from various planets, notably one known as Korender. His account involves a common interplanetary language called Galingua, which, is allegedly the source of Latin by way of ancient contact, or else has a common ancestor with Latin. Galingua and the language of Korender are both spelled alphabetically (with thirty-nine wholly novel letters with names bearing no relation to their phonetic values) and ‘phonetically’ (presumably this means ‘phonemically’); in Korendian, however, pronouns and numerals (cardinal and ordinal) are apparently represented logographically, with single symbols, despite being polyphonemic. Dean offers (often using non-standard terminology) a brief summary of Korendian grammar (very regular but otherwise suspiciously Indo-European in character, with only a few intriguing features) and punctuation, and a vocabulary.
Paul von Ward ascribes special status and universal applicability to the devanagari script used for Sanskrit and to the language itself. Like many non-mainstream writers on Indian matters, he ignores/rejects what has been learned about the Indo-European origins of the language, and he implausibly interprets Sanskrit and its script as the ultimate ancestors of all later languages and alphabets, which have allegedly deteriorated and suffered from loss of phonetic range and expressive power. He attributes the invention of devanagari to ‘Advanced Beings’, extraterrestrial or inter-dimensional beings whose activities are reflected in myths around the world. Von Ward is more widely read in linguistics (as in some other disciplines) than most such promoters of ‘ancient astronauts’, but his ‘understanding’ of the subject is very uneven and idiosyncratic.
One example of alleged extraterrestrial knowledge of ancient human languages involves the work of Paul Potter, who upholds the veracity of the very strange ‘messages’ which well-known abductee Betty Andreasson (now Luca) reportedly received (over a long period) from alien entities. Those which are not in English are simply strings of words familiar or otherwise, drawn (often with some distortion) from Latin, Greek and other languages; most of them are Latin or Greek words or English/pseudo-English words based or apparently based on these languages. Where a word exists in inflected forms in the source language, the citation (dictionary) form is virtually always the one which appears here, and there is no grammatical structure. The sequences do not exemplify language in use; they are lists of words. Potter translates the ‘messages’, adding grammar as is convenient to his proposed message. It is not at all clear why aliens would communicate like this; if they knew Latin or Greek, they could surely write in these languages. Human fakers (who may not actually be familiar with Latin or Greek but who could easily possess dictionaries and a conversion table for the Greek alphabet) must be suspected.
There are in fact other cases involving UFOs where a string of the citation forms of words taken from a foreign language is presented as if it were a meaningful sentence. One such case arose in the Garden Grove abduction case of 1975, later acknowledged as a hoax. The sequence (allegedly channelled) was nous laos hikanō (early Greek: ‘mind’, ‘people’ as in we the people, ‘[I] come’). A gloss ‘I come in the mind of man’ was offered; but all three forms are citation forms, and the grammar has merely been added by the translator. (See Larson, 2002.) Another case involves what appears to be a single Modern Greek word (in Greek script) in the written material displayed on artefacts supposedly associated with the Roswell Incident/Alien Autopsy case. However, the word includes a common spelling error grounded in the ignorance of many less-educated native speakers about the origin of the form. This again suggests the possibility of fakery.
Other UFO advocates also proclaim human languages (ancient or modern) as currently used by aliens. Often, the actual origin of the favoured language is said to be extraterrestrial (which would obviously require adjustment to accounts of the relevant human language ‘families’). The best current example is the Aetherius Society, founded by George King. The Society – like von Ward (see above) and other non-mainstream writers on India – ignores what has been learned about the Indo-European origins of Sanskrit, and regards it not merely as the ancestor of all human speech but as vastly ancient and the main lingua franca of a whole series of inhabited planets. They consider that it was ‘scientifically and metaphysically’ devised and is derived from fifty primeval sounds (which, by way of misconceptualisation, they confuse with the ‘alphabetic’ letters used to write the sounds of the language); these sounds themselves are derived from features of the Chakras (supposed energy vortices in the ‘subtle’ body of a human being).
The extraterrestrial ‘master’ Aetherius was extensively channelled by King, providing links with this complex inhabited universe and normally using King’s own Southern English English. The skeptical astronomer Patrick Moore exposed King’s claim that Aetherius/King could handle questions in any human language; the medium was nonplussed by very simple questions in Norwegian and even French.
As matters stand, the provisional skeptical conclusion on the reality of extraterrestrial languages (spoken and/or written) and on extraterrestrial knowledge of human languages must be that no known case is truly convincing.
As ever, detailed references on request. More next time!
Mark
Skeptical Humanities 
Every time I read one of these articles it makes me want to try and create a (comparatively) plausible alien language, because the world deserves better hoaxes.
As far as attributing human languages to aliens goes, I’d skip the Indo-European languages and go straight to Sumerian. There are way fewer people who can prove you’re misusing it than Latin, Greek, or Sanskrit! And we don’t know a damn thing about its origins — too far back in history — so nobody can say “no, it didn’t come from aliens, it came from this parent language.” Plus you could jump on the whole Zecharia Sitchin bandwagon if you want to.
In the 1980s the science-fiction roleplaying game Traveller introduced as part of his background a bunch of aliens called the Vilani, who were humans transplanted to other planets thousands of years ago; Vilani were given names based loosely on Sumerian. There was an attempt to invent the Vilani language in detail but it never got very far.