「好きな」は「favourite」? | The logic behind using "好きな" as "favourite"
I've seen on a few Japanese sites that you use 好きな to write "favourite" but I've never understood the logic behind this as this would literally mean "the (thing) that is liked" wouldn't it?
The reason I'm asking this is because I got asked a question "好きな日本語は?" in an IM tonight which threw me almost completely off. I can only assume the actual meaning behind this was "What's your favourite thing about Japanese?" looking back at the context that came after it.
But yeah, if someone could clarify up the logic behind using 好きな that would be great, especially as what confuses me is if you'd want to say something like "the book that I like is awesome" or something like that. Would it just be context that differentiates it from meaning "favourite" then?

Question

「好きな」は「favourite」? | The logic behind using "好きな" as "favourite"
I've seen on a few Japanese sites that you use 好きな to write "favourite" but I've never understood the logic behind this as this would literally mean "the (thing) that is liked" wouldn't it?
The reason I'm asking this is because I got asked a question "好きな日本語は?" in an IM tonight which threw me almost completely off. I can only assume the actual meaning behind this was "What's your favourite thing about Japanese?" looking back at the context that came after it. 
But yeah, if someone could clarify up the logic behind using 好きな that would be great, especially as what confuses me is if you'd want to say something like "the book that I like is awesome" or something like that. Would it just be context that differentiates it from meaning "favourite" then?

Answer

No need to say, there is no adjective form of the word LIKE when to mean like-like. Also the word FAVORITE posses two usages; noun (this is my favorite), and adjective (this is my favorite music). 好きな is the adjective form of the verb 好き. If you say FAVORITE as a noun in Japanese, it should be 好きなもの. You know these right?

The original message 好きな日本語は? seems to be too colloquial and missing the actual object of the sentence. Here 日本語 should’ve worked to modify the missing object 言葉. Your friend actually asked you what’s your favorite Japanese “word/phrase”; 好きな日本の言葉は何ですか. No wonder you got confused.

This is the book I like. // これがぼくの好きな本。
This is my favorite book. // same as the above
This is my favorite. // これがぼくの好きなもの。
The book I like is awesome. // ぼくが好きな(この)本は最高。
My favorite book is awesome. // same as the above

Answer

As you said, "好きな" literally means "things you like". But we usually talk about our favourite things when we introduce ourselves, so we usually answer one or a few favourite things to the question.
The word "favourite" has a few Japanese translations, such as "大好きな" and "一番好きな", but sometimes they might sound a little unnatural.
Here are examples:
http://ejje.weblio.jp/sentence/content/favorite

By the way, I wonder if "What's your favourite thing about Japanese?" has the same meaning as "What's your favourite Japanese word?"