Acc. to http://www.focloir.ie/ga/dictionary/ei/leave fág is ok.

I can't find any example of "fág" used without an object in Ó Dónaill nor in de Bhaldraithe. Maybe they've accepted that wrong new use of "fág" in the new dictionary, because so many non-native speakers say it because they don't master the difference between imigh and fág, since English only has "leave" for both. But accepting learners' mistakes in a dictionary is not a good thing, in my opinion. Imagine if they accepted French people's mistakes in the English dictionaries. It would be ridiculous.

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Is fearr Gaeilg na Gaeltaċta ná Gaeilg ar biṫ eile
Agus is í Gaeilg Ġaoṫ Doḃair is binne

Alas, it seems to be very common in Irish. Something to do with keeping it 'modern' for the learner...

From my "semi" native experience, fág without an object sounds very alien to me. I've never used it in speech, nor have I ever seen it in writing. FWIW anyway...

In English, there's a difference between "leave behind" and "go away." Would it be fair to say that that's the same as the distinction between "fág" and "imigh"?

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Táim ag foghlaim fós. Fáilte roimh gach aon cheartúchán.

yes!



ie. To Anglicize Irish so that it's easier to learn for native English speakers.

As John Ghráinne used to say, "Sílim go mairfidh an Ghaeilg ach ní thuigfidh mé níos mó í." (or something like that).

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Is fearr Gaeilg na Gaeltaċta ná Gaeilg ar biṫ eile
Agus is í Gaeilg Ġaoṫ Doḃair is binne

There is this example in Ó Dónaill:
http://www.teanglann.ie/en/fgb/f%C3%A1g

Agus Foclóir Phádraig Uí Dhuinnín:

Chan fhacaidh mé 'n cionn sin.

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Is fearr Gaeilg na Gaeltaċta ná Gaeilg ar biṫ eile
Agus is í Gaeilg Ġaoṫ Doḃair is binne

Idiomatic structure can arise from ellipsis.

Think of English He is [in a state of being] good or I'm here for [to get] a piece of cake

Also:
for [to help] him
for [the benefit of] the team
for [the duration of] a week
for [reasons of] honour
for [the amount of] a pound
good for [the body of] you [?]
for [the time of] Winter, it's lovely!

See in Irish:
chuaigh sí fá choinne bainne a fháil clipped to chuaigh sí fá choinne bainne

There is also metaphoric usage Cheannaigh mé ar phunt amháin é (and i don't know if 'ceannaigh' is related to head either (to think before acting?)

Since 'ann' is used for state, then one can say you are in a state of being able to speak Irish if you are in ann Gaeilg a rá

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__̴ı̴̴̡̡̡ ̡͌l̡̡̡ ̡͌l̡*̡̡ ̴̡ı̴̴̡ ̡̡͡|̲̲̲͡͡͡ ̲▫̲͡ ̲̲̲͡͡π̲̲͡͡ ̲̲͡▫̲̲͡͡ ̲|̡̡̡ ̡ ̴̡ı̴̡̡ ̡͌l̡̡̡̡.___

Actually, we've been living with French people's mistakes since 1066.

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Múinteoir Gaeilge - Irish Teacher
My "specialty" is Connemara Irish, particularly Cois Fhairrge dialect, but I can also speak Ulster and Munster Irish with native-level pronunciation.
Is fearr Gaeilge ḃriste ná Béarla cliste, cinnte, aċ i ḃfad níos fearr aríst í Gaeilge ḃinn ḃeo na nGaeltaċtaí.
Gaeilge Chonnacht (GC), go háraid Gaeilge Chois Fhairrge (GCF), Gaeilic Uladh (GU), Gaelainn na Mumhan (GM), agus Gaeilge an Chaighdeáin Oifigiúil (CO).