Only tangentally related to Irish, but...

I'm being interviewed for a job which requires the use of a language other than my native Báerla - French. Now I'm nearly fluent in French and I've been learning it since I was a buachaill beag óg, but it isn't my native tongue and I do have to put slightly more effort into speaking it than I do English.

Now I'm daily studying Irish, so I'm a little worried that all of a sudden my mind is going to bring up random words in Irish and intersperse them with my French, or worried that my Irish is going to crowd out my French. The linguist in me is saying that this is stupid and that French is ingrained enough into my head that I'll be fine.

But does anyone else have experience with this? With one language providing interference with another? One example, I was using the little German that I have and I accidentally said 'agus' when I meant to say 'aber'..which was embarassing, to say the least.

The first time I started learning more than one language at once was at university. I had a little French from school and I took on German, French and Japanese at uni. This involved switching between the languages every hour or so. I would sometimes slip up and say "ja" to my Japanese teacher, "oui" to my German teacher, and "hai" to my French teacher, etc., every now and again near the beginning of each lesson.

This was quite unsettling at first but after a while it all sorted itself out and I was able to keep them from interfering with each other without thinking about it.

I still find it hard to switch languages midsentence, such as when you quote some English in the middle of a French sentence. I think the base position the tongue may sometimes be slightly different for each language and you get into the "flow" of the language by adopting that position, I find it hard to break from that position to switch to the other language and back again quickly.

On the other hand, an English friend of mine could tell a joke about a conversation involving three different dialects of English and not get the accents mixed up, something I can't do myself. I can mimic other accents of English but once I am "in" one I can't chop and change to another that easily.

Anyway, back to your original question, the more confident you get in each new language, the easier it should become to keep the others from interfering with it.

I think you'll be grand. I was studying Irish, French and German at one stage in secondary school and I interchanged words a few times but I wasnt particularly (anywhere near) fluent in any of them.
As you're basically fluent I wouldnt worry about it if I was you.

I studied language contact phenomena and I worked as a language teacher for quite a while.
Just off the top, I would suggest immersing yourself in French (conversation / reading / radio listening or TV watching)for a time before your interview.
I'm finding the same phenomenon happening with me now between Irish and Welsh. I don't have the problem between French or German, however.
I think, if I remember correctly, this has to do with frequency of use and personal and/or cultural meaningfulness of the item.
Any other ideas?
Slán agaibh.

Many years ago (thirty in all I'm afraid) I was quite fluent in Flemish which is a dialect of Dutch but alas I have forgotten most of it now from lack of practice but still some words come out when I'm speaking Irish espeicially when there's a few pints of the black stuff involved.

I find that what I would call the "oral sound-delivery-system" has a bigger influence as regards getting different languages tangled up than their actual linguistic proximity. German and Irish, I find, have this same kind of "oral sound-delivery-system". French and Irish are further apart in this regard, in my very humble opinion. If you want to be on the safe side, occupy yourself solely with French for a few days before the interview.