Out of all of
Tolkien's languages, Entish is without a doubt the one we know the
least about (with the exception of those
languages that we know
nothing about.
Taliska comes to mind. (
The Lost Road, 182-217,
Lhammas)) Part of the problem is that Entish, being the language of huge
treelike creatures, is completely impossible to represent in
Roman (or for that matter, Elvish) script. Entish was full of subtle tones (like Chinese, but Entish probably had in excess of 100 tones) and other sounds which simply aren't present in the languages of any other race.
We may perhaps get some idea of what Entish was like from the way they use Quenya, an Elvish tongue that they seem to have a preference for. It appears that the Ents simply use Quenya words and adapt it to Entish grammar, resulting an a very long, redundant phrase. Examples of this include laurelindórenan lindelorendor malinornélion ornemalin which is translated as 'The valley where the trees in a golden light sing musically, a land of music and dreams; there are yellow trees there, it is a tree-yellow land.' (Letters:308) and Taurelilómëa-tumbalemorna 'Forestmanyshadowed-deepvalleyblack Deepvalleyforested Gloomyland' (there is a black shadow in the deep dales of the forest) (LoTR III: Appendix F).
Frodo did attempt to represent an Entish phrase: A-lalla-lalla-rumba-kamanda-lindor-burúmë (LotR p. 1105). However, Tolkien himself states that this is probably innacurate, for the reasons mentioned in the first paragraph. According to Helge Fauskanger, 'We cannot analyze this fragment.'*
For more information, see Ardalambion's page on Entish at http://www.uib.no/People/hnohf/entish.htm and Compte-rendu du Dictionnaire des langues imaginaires at http://www.geocities.com/almacq.geo/temp/crdictli.html (if you read French).
(*)Helge Fauskanger, Ardalambion (http://www.uib.no/People/hnohf/entish.htm).