Would you consider it an ultimate compliment if a native speaker of a foreign language told you that you sound sexy speaking it? ~

I might be suspicious.

I don't think accents make as much difference as the timbre, pitch, rhythm, and modulation of the voice.

I was at an Russian Orthodox Easter dinner once with my grandmother when I was 16. This Russian guy came up to me and asked me my name in Russian. I answered and thanked him in Russian for asking. He said I pronounced thank you wrong. ;(

depends on who said it

I would feel complimented, indeed, yes. Especially if the guy who said it to me was the guy in your image.
;)