I heard that a native speaker of a language frequently has a vocabulary of 50,000 words, although what is a word is a debatable question. Now most elementary language books, eg Ó Siadhail's Learning Irish, introduce 1800 words.

* The Chinese government has produced a list of 8840 words using 2,907 characters, organised into A, B, C and D lists of broad frequency, that foreign learners should master to get the Advanced Chinese Proficiency certificate.
* The Russian Learner's Dictionary by Nick Brown has 10,000 words organised by frequency. Brown says in the preface that no more words are needed by a foreign learner. Words like дятел ("woodpecker") are not in the list, but as he says you could read Russian for years without coming across this word, and so learning more words is unlikely to be worth it.
* There is a list of 9985 Finnish words organised by frequency at http://www.csc.fi/kielipankki/aineistot/ssts/index.phtml, but I think it is biased towards newspapers and includes many proper nouns, eg Zyuganov.
*There is a list of 10,020 words in Finland Swedish organised by frequency at http://www.csc.fi/kielipankki/aineistot/fsfo/index.phtml. Once again I think it contains proper nouns.

Is there any such list for Irish anywhere? Do forum users have a handle on how good a person's Irish would be with 10,000 words?

One thing about Irish is that it's very idiomatic.

You might now that:

aghaidh = face

but then you'll see the likes of:

Chuaigh sé ar aghaidh = He went forward


(Because your face is at the front!)

I think the Maynooth scheme works on this principle:

http://communications.nuim.ie/press/020305.shtml

Someone posted a thread here awhile back linking an article that said you need 10,000 words for fluency … you could try looking for that. I'm curious though: isn't the word dyatel used to refer to an annoying, pressing, nosy person or something similar? I recall having this discussion with someone while in Ukraine …

Is mór an crá iad cnagairí! Nach cuimhin leat Woody an Cnagaire?

http://www.woodywoodpecker.com

Why don't you just check the number of translations on a dictionary? Most of them boast a figure on the back. However, as you know, due to references, placenames and "makey-uppy" words you may want to take 65-ish% as the answer. Have you tried asking BnaG?

The Maynooth scheme sounds like tests for an official certificate of fluency in Irish will eventually be provided.