要俾一個母語係廣東話嘅人檢查吓。 :)

佢啲母語 → 佢嘅母語

(When describing possession, 啲 is usually used for plural nouns only)

Thank you!

I was misled by this example in CantoDict:
http://www.cantonese.sheik.co.u.../examples/291/ [我啲廣東話好到你唔信呀！]

But, after all, how do I know if this example is correct?

This one will be a bit tricky to explain, but I'll try my best ;-)

In the case of 我啲廣東話好到你唔信, 啲 is used instead of 嘅 because 廣東話 is treated as a 'complex' object (as opposed to a single entity); when you say you're good at a certain language, you usually don't mean you're good at one single thing but in a wide range of aspects like speaking skills, listening skills, vocabulary, etc.

However, when talking about one's mother tongue, languages are treated as distinct, single objects; English is English, French is French, Cantonese is Cantonese. The only thing that is relevant is the language itself, and all the other details or aspects are unimportant. Therefore, 嘅 needs to be used rather than 啲.

(I'm not sure if this applies to other languages, but this is how it's usually interpreted in Cantonese)

Oh. Thank you, I think I've understood. ^^