"He likes you."
Translation:Mae o'n licio chdi.
Depends. Kids who go through Welsh medium education but don't grow up in Welsh speaking homes (or grow up in homes where the parents can speak Welsh, but don't) are likely to because they'll learn lots of different words from their various teachers. Those who are first-language Welsh probably don't.
They are - and the fact that you try speaking Welsh as a foreigner is welcomed warmly (even when you make mistakes every now and then). Mixing dialects is ok as a starter, at least - though they might point out that a word you used was s/n and say the word they normally use themselves. I heard a few choir friends speaking Welsh in the south and surprised them by saying "dw i'n deall", and they were much impressed and then told me that I had used the northern version and that they said "rwi'n dall". All very friendly - so do try speaking when you get a chance! :-D