As a learner I'm happy about every word or phrase I already know from another language - because it is easier to remember them.
Language purism is something I leave to native speakers (which usually aren't puristic at all ...)
There are thousands of original words and idioms without any resemblance with my native language and often even with a different range of meaning. So there is enough to learn.

To reply to a "go raibh maith agat" in every day conversation often needs rapid response.
So it is difficult to remember and recall (!) a phrase as "go ndéana a mhait duit"
(I often enough say even "please" in English despite all resolving to use an idiomatic phrase because the usual German reply is "bitte" which comes naturally without any thinking. So, I'd really be glad if such a "Germanicism" would exist )

Lughaidh - I grew up in the 1940s and 50s and spent most of my Summers around Cnoc na hAile (near Inverin). This was before deBaldi published his dictionary - a book I have never liked - and before anyone heard of Standard Irish. So a lot of my language is now rather old fashioned and I have been
told more than once by newbies that much of it is incorrect because it does not comply with the Standard version. I am of the opinion that all language is correct if the hearer understands what is said. A problem arises when Irish is used as a hammer, either to show off or to undermine the speaker - an attitude
quite common among a certain type of know-all. So if someone says Tá fáilte romhat to me I accept on two levels - 1. I understand whats being said and 2. good manners and courtesy decrees that the speaker
speaks from their own understanding of the language and must be respected for their effort.

Now where has all that come from..I must go and lie down!

I am not. Being understood is easy, if you say "tá sé fear", people understand you... What is correct is what is considered as correct by the native speakers of the dialect, ie. what they would naturally say themselves.

Btw, I forgot to mention another way to say "you're welcome" : níl a bhuíochas ort.

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

It seems that Donnegal speakers (and learners under their influence) are more likely to be very insistent that Tá fáilte romhat is an Anglicism and only Go ndéana a mhaith dhuit is correct.

Connemara speakers use Tá fáilte romhat almost exclusively, rather than Go ndéana a mhaith dhuit.

Wombat once pointed out that the first verified use of "You're welcome" in English literature only appeared c. 1906.

When I was a boy, nobody said "You're welcome" in Australian English, most people said "My pleasure" in formal contexts (and "No Worries" in less formal contexts). It was a string of MacDonald's commercials in the 1970s that really established the Americanism "You're welcome" in Australia.

On the other hand, Irish has another phrase that uses fáilte and has nothing to do with English "welcome". That is the appending of agus fáilte to show enthusiam or willingness for an action, Déanfaidh mé dhuit é agus fáilte. "I'll do it for you willingly."

It is not impossible for Tá fáilte romhat to have developed from that sentiment.

So I wonder just how much of an Anglicism Tá fáilte romhat really is? (I also wonder how far back Croeso goes in Welsh?)

I personally think it could be the other way around, i.e., that English may well have received this one from the Irish.

It really is a bit of a chicken and egg question.

In the end, so many people in Connemara use Tá fáilte romhat that it has gone beyond being an Anglicism (if it ever was one) and there isn't much point criticising it.

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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).

Idiom at a dyadic or exchange level ('tá fáilte romhat' or 'ciao' etc), I don't think is such a big issue, as you are using stereo-typified forms, with little gramamtical analysis.

Tóg go bog é is a little worse, then táim suas faoi ('up for it') then bhí sé ag bualadh mé and so on get much more dangerous.

By the way, has anyone ever heard a shortening of 'go ndéanaí a mhaith duit' to 'néanaí a mha' it' (or similar)?

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

Speaking of "purism" has anyone else read what this guy had to say on the subject?

https://wordotter.wordpress.com/2013/09/15/irish-language-puritanism-or-why-browsing-language-forums-makes-me-want-to-strangle-people/

If so, what might your thoughts be?

Níor bh'fhéidir liom aontú leis níos mó.

Go raibh míle maith agat.