"This looks delicious"
Kore-wa oishi-sou desu.
Notice the shortening of the "i" vowel of "oishii". If you don't shorten it and instead say "Kore-wa oishii sou desu" it means "I've heard that this is delicious".
-sou attached directly to an adjective is very useful for expressing the "X looks --" idea.
More examples:
"Sono resutoran-wa taka-sou desu" -> That restaurant looks expensive. ("takai--> takasou")
"Kono natto-wa mazu-sou desu" -> These fermented soybeans look like they taste awful. ("mazui"--> mazusou")
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"That sounds Japanese"
Sore-wa nihongo ni kikoemasu.
Notice the use of "kikoeru" instead of "kiku". "kiku" means to listen to or to hear. "kikoeru" means "can be heard" or, in this case "to sound (like)".
Also, "sore-wa" is good here, rather than "sonna". "sonna" is usually followed by a noun phrase, or a nominalizer.
"Sonna koto nai yo!" -> That's not true! (lit. 'It's not that thing')
"Sonna-no wakaranai yo!" -> I don't know that (sort of thing - "no" is a nominalizer here)
If you want to use "sonna" as an intensifier preceding an adjective, you add "ni" before the adjective:
"Sonna-ni samui tte souzou shinakatta." -> I didn't imagine it would be that cold.
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Your avatar says "nihonjin kanojo boshuu-chuu"-> I'm in the market for a Japanese girlfriend (lit. I'm recruiting a Japanese girlfriend).
Cute