On our ninth au pair in as many years.
None have shown a wit of interest in DH - plenty have been objectively very attractive. God forbid there is always a first time but in my experience it is many thousands of times more likely they will get on a DH's nerves than be an attractive prospect. I wouldn't give it a second thought.
With both DCs in school/having long days, the AP is now more of a babysitter for DDog and does about 15 hours a week after school for us. For several years our AP worked alongside a nanny in a share we had.
Do you actually need childcare help? I am not sure how much of the language your DDs will learn.
We will get one next year who speaks the target language DD needs for GCSE. Considering that we don't speak this language AT ALL, even a bit of homework help would be great.
If you don't need childcare help to get to work, and unless you have a vast property to ensure some privacy, I wouldn't commit to a lengthy au pair stay just to get a bit of language help. Some do want three months - you could see how it goes. Or perhaps try a summer au pair but then think about whether they'd expect to come on a holiday with you.
Their skills in most areas you need them for - childcare and say cooking a light meal - can be very basic and you need to assume they will need quite a lot of oversight. Ours have never cleaned but people I know who have asked for this tend to be underwhelmed. I am always amazed when people hand their 19 year old APs cook books and think they can get on with something complicated.
It really can really, really impinge on your 'me/down time'. It's been a while since we've had this issue but there was nothing worse than coming home from work, catching up with the kids, etc and being met with the expectation that it was socialising time as far as the AP was concerned, even though it was half past nine or later. This was very hard and after one really trying year we ended up having to set ground rules. But I do walk around in my PJs still!