If a foreign speaking person works for you and you thank them in their own language...

[Kablooie]

is it respectful or condescending?

[steve2470]

1. My son would say condescending but meh

I think if you say the correct words or phrase, it's a nice thing to do.

[geardaddy]

2. I think it depends on the person you're thanking.

Some people might appreciate the gesture, some might be annoyed that you think of them as a foreigner.

[Wounded Bear]

3. I think it depends on your attitude when you say it...

And the general condition of the employer/ee relationship.

Sometimes all you have to do is ask...."Does it bother you when I do that?"

[NewJeffCT]

4. It probably depends on the individual's culture and the individual

My wife is Chinese and she'd be happy if somebody did that. Of course, that doesn't mean it applies to every Chinese person, either.

What pisses her off is if somebody tells her, "your English is a lot better than my Chinese." Her spoken English is generally very understandable, but sometimes she doesn't understand all the idioms, and sometimes has trouble understanding English when it's not spoken with an American accent.

[Iggo]

5. Long as you know what you're saying and you know how to say it...

...I don't think it's a problem.

[Aristus]

6. My assistant is Russian.

She likes it when I greet her in Russian. Especially since she knows I like the language, and am interested in learning more of it.

I don't know why anyone would be offended if someone were to reply in the language spoken, unless the person doing the reply was obviously and intentionally using a parodic form of the language.

For example, a tanker I used to work with in the Army would thank people, not necessarily Hispanic people though, by saying broadly: "Moo-cho grassy-ass, Pedro!"

I'm not Hispanic, but if I was, I would think that was intentionally insulting.